[FEATURE]: Small changes to Inhomogenous_incoherent_process that would improve usability

[Lomholy]

Is your feature request related to a problem? Please describe.
When building a simulation of an electrolyzer using the inhomogenous incoherent process, I often found myself in need of the following things:

1. A Heavyside like function, that does something like: H(x,t,a,b) -> if (x<t) return a, else return b
2. The exponentiation order in tinyexpressions seem to be performed in the "Unnatural" order for physicists (and just, math in general??). This can be changed as per https://github.com/codeplea/tinyexpr/tree/master#:~:text=If%20you%20would,g.%20Python%2C%20Ruby).
3. A shorthand function for a gaussian distribution in tiny expressions would be immensely useful.

I will implement these myself when time permits.

[Lomholy]

With #2463 These have been added.