Improve Export

[Floha258]

The export currently downloads a file of the complete state, which includes a bunch of useless information and has a lot of overhead.
The export should only include items, locations and settings in an ideal world. That way we can also decrease the size of the exported file by a lot and won't end up with a 12MB large export file.

[cjs8487]

Part of the reason the entire state is exported is to avoid having to reconstruct logic from the repository, which prevents exports from being broken by upstream changes (i.e. adding/removing checks or changing requirements). This should be improved naturally as a result of the planned updates to the sourcing mechanism (by allowing the tracker to fetch datafiles for any point in the upstream, including forks)