Defragment IGUIButtonBehavior Settings.

Moves the AddSetting sound calls from CButton and CCheckbox to IGUIButtonBehavior, since the latter is the only class to use them.
Moves ChooseColor from IGUIButtonBehavior to CButton, since that's the only class to use it and the only class registering the dependent Settings following rP14476 (refs rP22952 / D2314)

Initialize m_PressedRight in the constructor to prevent undefined behavior in possible future code following rP13040, refs #1028.
Remove unused soundPath variable following rP22756 / D2209.

Differential Revision: https://code.wildfiregames.com/D2318
Tested on: clang 8.0.1, Jenkins