Mod Config loader + Extra Mod Tabs

[GauntletGames-2086]

Adds a mod config loader (defined through --- MOD_CONFIG_PATH, can also be defined through SMODS.current_mod.mod_config or SMODS.Mods[<mod ID>].mod_config) and 3 tabs to mod button.

• "Additions" shows all the objects added from the mod.
• "Credits" shows the credits for the mod. Defined by SMODS.registerCreditsElement.
• "Config" shows the settings page for the mod. Defined by SMODS.registerSettingsElement.

TODO:

• All features complete!
• Cleanup and refactor create_UIBox_mods (it's cluttered now and doesn't need to all be stored inside the create_tabs function)
• Redo "Credits" setup
• Check to hide "Additions" tab if no objects are added
• Verify "Additions" works correctly (this would include 0.9.8 mods)
• Add "Other Objects" button to store custom collections to both main collections and Addition tab.
• (Potentially) add "Config" tab
• Fix back_func issues.

[GauntletGames-2086]

Alerts should be fixed now.