typos, formatting, gitignore and eventhandlers

Just changed a few basic things to get things to work on my end. Also added/changed some minor event handling functionality in Button and Textbox; you might need to alter your Button event handlers slightly in Instincts.

I've also refactored the MenuItem hierarchy a bit; reused parent stuff, added common constructors and removed some redundant variables. Main change is that Image is now the parent of anything requiring at least 1 fill texture (since the functionality is the same).

Next I'll get stuck into resolution-independent widgets, then sound stuff.