EMSUSD-1521 refactor AE template

[pierrebai-adsk]

• Move each custom control to its own file.
• Rename custom control and their file to follow the same pattern.
• Move the creator function to static function in the corresponding custom control.
• Move some helper functions to their corresponding custom control.
• Rename some parameters to have clearer name (attrNames instead of controls and attrName instead of c).
• Document how the AE template code works.

[pierrebai-adsk]

While the change may seem big, most of it is simply code that was moved out of the ae_template.py file into their own file. There is no new code in the new files. (Other than making all the custom control class names follow the same naming pattern.)