Added fromName to FlxColor

Create ```FlxColor.fromName()``` per https://github.com/HaxeFlixel/flixel-ui/pull/68
Utilizes reflection to allow mapping from string names (such as BLUE and YELLOW) to FlxColors. 

Of course, there's still a couple minor tweaks available depending on what's desired:
 * handling of lowercase names
 * handling of misspellings (such as BLU)
 * handling of GRAY/GREY (per https://github.com/HaxeFlixel/flixel/pull/1233, probably should add GREY for those who want it).