TextEdit: implement the caseformat field

[lynxlynxlynx]

Currently not read, but you'll find a comment in CHUImporter where that can be added.

It can have the following values according to NI: 0 - normal, 1 - upper, 2 - lower. If 1 or 2 is set, the opposite case is automatically converted to the other, input is not blocked.

[bradallred]

we can expand TextEditFlags with these bits

enum TextEditFlags {
	// !!! Keep these synchronized with GUIDefines.py !!!
	Alpha = 1,		// TextEdit accepts alpha input
	Numeric = 2 	// TextEdit accepts numeric input
};