[docs] Game_Control should be a subpage of skin_controls

[enen92]

Description

Right now the game control doxygen page is shown as a menu entry on doxygen side bar. It should be in fact grouped with all the other skin controls.

Motivation and Context

Proper documentation for Leia. Group all skin controls on the same place.

How Has This Been Tested?

Compiled docs and manual testing

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed

[garbear]

I noticed that the Game Control is missing several parameters (<videofilter>, <stretchmode>, <videorotation>). I'll try to add these and their possible values.