Finalized POC of 4-state game

Game has now 4 states: mainmenu, credits, strategy, combat

You can enter all modes from mainmenu, although strategy and combat are empty and you can't come back
You can go to credits and with click you return back to main menu

Image loading: NOTICE: Images can be only loaded in erisgame.js. This needs to be fixed (or found out if this is unfixable)

Unloading: Works now, but you have to be extra carefully that you actually unload everything. Unload doesn't throw error if you try to unload null

Other modifications:
- Wade upgraded from 1.3.3 to 1.4.0
- Animation used
- Correct way of doing non-inline event handlers (check mainmenu.js)
Merge branch 'development' into two-state-game