Bunch of changes:  minor bugfixes, tile test additions, fixed checkbox default text color glitch
updated flixel-ui with latest changes from flixel. Will probably need further polishing, this gets my project to compile, and I dont notice any issues.
Small changes - created an "addAsset()" function and various other sundries.
Added data/definition consolidation and deprecated "9slicesprite" tag, use "chrome" instead, or "nine_slice_sprite"
Added FlxUIDropDownMenu - only works in code for now, will add xml loading logic later.
Minor tweak
Fixed velocity in FlxUIGroup
Merge remote-tracking branch 'gltovar/dev' into dev

Conflicts:
	flixel/addons/ui/FlxUI.hx
	flixel/addons/ui/FlxUITabMenu.hx
Fixing up flixel-ui for upcoming flixel release
safety check for FlxUIButton
Fixed some logic errors in button loading w/ regard to 9-slice-scaling. Now throws error if you provide only one asset but no src_w/src_h.  XML loading is unchanged - it now deduces the proper src_w/src_h values for an "all" tagged graphic asset.
Added basic icon support to FlxUIButton.

Using these methods:

addIcon( icon:FlxSprite )
removeIcon()
changeIcon(newIcon:FlxSprite)