Fix filenames to match wp core coding standards

File names currently use "dots" `.` to separate words, this should follow the standards documented at https://github.com/gocodebox/lifterlms/blob/master/docs/coding-standards.md#file-names

Since we have several hundred incorrectly named files our strategy for updating the file names is as follows:

+ Any new files added should be named according to the new standards
+ Legacy files can be updated as they are edited or modified taking care to ensure `include`, `require`, `include_once`, and `require_once` references to these files are updated in tandem.
+ Additionally we must be careful to ensure that renamed files are not included from outside the plugin (in themes, add-ons, etc...)
+ Communication should be made to 3rd party developers when files are renamed to ensure they have an opportunity to update their includes should they be including core files