Qt: Fix some options not changing enabled status on game start.

QCheckBox::toggled and other similar signals are used to save changes and to update widget status (such as enabled).. OnConfigChanged needs to load new values and trigger widget updates, but the new value shouldn't trigger a save. A save is unnecessary (the config has the correct values and the UI is being updated to those values) and it'd trigger another ConfigChanged signal.   This commit blocks the save without blocking the signal entirely.

Creates a layer outside the game config layer system and passes it to the created gfx widows, so as to not interfere with the global config system.

Supports multiple game properties being open at once.
Supports editing while a game is playing, but the options only save and update the active game when the window is closed.
Right-clicking will remove a property from the game ini.

This reduces code duplication in the different ConfigControls. This is
helpful for the next commit, which will modify the now deduplicated
code.