Fixed name collision in class factory definition

[vhaasteren]

This PR fixes #344. Inside the class factories, the class names now have a trailing underscore. This is not a user-facing change.

The main problem is that if you try to access attributes of the function (the class factory) itself, you get an UnboundLocalError, because the class that has the same name is in this scope and has not been defined yet. Making the names differ fixes that. A reason to access attributes of the class factory would be to get static variables, so one could for instance issue a warning only once, rather than every time you call a class factory. This can be done with global variables also, but it's less neat.

Currently, this PR is not exhaustive.

[codecov]

Codecov Report

Merging #345 (71caf7e) into master (5ef5ff4) will decrease coverage by 0.01%.
The diff coverage is 93.75%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #345      +/-   ##
==========================================
- Coverage   88.37%   88.37%   -0.01%     
==========================================
  Files          13       13              
  Lines        3012     3010       -2     
==========================================
- Hits         2662     2660       -2     
  Misses        350      350              

Files Changed	Coverage Δ
enterprise/signals/parameter.py	84.05% <75.00%> (ø)
enterprise/signals/deterministic_signals.py	100.00% <100.00%> (ø)
enterprise/signals/gp_signals.py	90.68% <100.00%> (ø)
enterprise/signals/selections.py	90.41% <100.00%> (ø)
enterprise/signals/signal_base.py	90.11% <100.00%> (ø)
enterprise/signals/white_signals.py	98.47% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[vhaasteren]

I'm closing this PR. It's not necessary