Update issue templates (#343)

* Added three types of issue templates
* Added pull request template

Author: vkresch

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: bug
+assignees: ''
+
+---
+
+#### Describe the bug
+A clear and concise description of what the bug is.
+
+#### Describe how to reproduce the bug
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+#### Describe the expected behavior
+A clear and concise description of what you expected to happen.
+
+#### Show some screenshots
+If applicable, add screenshots to help explain your problem.
+
+#### Describe the OS you are using
+ - OS: [e.g. iOS, Ubuntu 18.04, Windows 10, ...]
+ - Language: [e.g. C++, Python, ...]
+ - Version [e.g. 3.6.8]
+
+#### Additional context
+Add any other context about the bug here.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: feature request
+assignees: ''
+
+---
+
+#### Describe the feature
+Is your feature request related to a problem?
+A clear and concise description of what the problem is. 
+Example: I am always frustrated when [...].
+
+#### Describe the solution you would like
+A clear and concise description of what you want to happen.
+
+#### Describe alternatives you have considered
+A clear and concise description of any alternative solutions or features you have considered.
+
+#### Describe the backwards compatibility
+How does the feature impact the backwards compatibility of the current major version of OSI?
+If the suggested feature would be implemented would there be an issue with the previous versions of OSI? What part of OSI would break or improve by this feature?
+
+#### Additional context
+Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/question.md

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+---
+name: Question
+about: Ask a question if you do not understand something or just want clarifications.
+title: ''
+labels: question
+assignees: ''
+
+---
+
+#### Describe the problem
+I want to do ... in my application, but what I am actually getting is....
+Here is a screenshot that illustrates the problem:
+
+`image.png`
+
+#### Describe what you have already tried
+This is the most simplified version of my code that I have been able to get, which still produces the problem I described above.
+
+    // my code
+    ...
+
+Basically, what the code is doing is....
+Changing ... does not work because it gives the following error:
+
+
+    Some error
+
+
+#### Describe your research
+[The documentation here] mentioned ... but did not provide a clear example of how that is done.
+[This Stack Overflow question] describes a similar problem, but mine is different because....
+
+#### Ask your question
+So my basic question is, how do I...?
+
+#### Additional context
+Add any other context or screenshots about the question here.

.github/pull_request_template.md

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+#### Reference to a related issue in the repository
+Add a reference to a related issue in the repository.
+
+#### Add a description
+Add a description of the changes proposed in the pull request.
+
+**Some questions to ask**:
+What is this change?
+What does it fix?
+Is this a bug fix or a feature? Does it break any existing functionality or force me to update to a new version?
+How has it been tested?
+
+#### Mention a member
+Add @mentions of the person or team responsible for reviewing proposed changes.
+
+#### Check the checklist
+
+- [ ] My code and comments follow the [style guidelines](https://opensimulationinterface.github.io/osi-documentation/osi/commenting.html) and [contributors guidelines](https://opensimulationinterface.github.io/osi-documentation/osi/howtocontribute.html) of this project.
+- [ ] I have performed a self-review of my own code.
+- [ ] I have made corresponding changes to the [documentation](https://github.com/OpenSimulationInterface/osi-documentation).
+- [ ] My changes generate no new warnings.
+- [ ] I have added tests that prove my fix is effective or that my feature works.
+- [ ] New and existing unit tests / travis ci pass locally with my changes.