relax SVN archive

Modified, that the order of sorting models for auto_analysis, should be:

Analytical first, then silico, and then numeric.
After this, the year for implementation should come first.

This makes sure that CR72 is analysed first.

And also DPL94 will be sorted first.

Added unit tests regarding model.py and its functions.

Removed the unit test regaring model.py in test_variables.py.

Parted the file of variables.py into model.py.

Copied variables.py to model.py.

There should not exist any functions in variables.py.

variables.py should only consist of hardcoded variables, and the functions related to model sorting and nesting is split into its own file.

Modified in documentation, that the "No Rex" model have one chemical exchange site. Namely itself.

Added a "check" function, what will determine if R1 data is missing for a model to analyse.

Also added corresponding unit tests, to test the functionality.

Split the unit test of specific_analyses.relax_disp.checks.get_times() into its own unit test file.

Fix for correct English, replacing "where" with "whereby".

Renamed the parameter "r1_fit" to "r1".

This naming fits better to all other parameters.