ADD HYBRID GAUSSIAN FIT UNIT TEST
ADD DEFINITION OF HYBRID GAUSSIAN FIT MECHANISM
Remove hybrid gaussian mechanism definition

There is no need to define an entirely new mechanism. It's easier
to just call on separate mechanisms, this makes changes easier and cleaner
Separate the test for low vs high background

Separation of this test facilities means that all fitting mechanisms
will use a consistent test. This also means that one can test for bkg
modes outside of the fitting mechanism itself
Change function name to be consistent with previous implementation
Use IsLowBackground function
Remove unneeded message output
Use refactored IsLowBackground function
Remove unneeded message output
Remove old function calls from before refactoring of islowbackground
Add support for generic fit mechanism
Remove references used before islowbackground refactor
Change fitting parameters to force one narrow and one wide gaussian
Fix bug where the threshold and fit minimum were flipped when callid islowbackground
Add debug messages to show which mode is running
Update unit tests to testing root file
Exit if file is not opened correctly
Merge branch 'feature/singlegaushybrid' into develop