chat patch by Izy

chat patch by Izy

Provided by mynick1 on IRC,
whitespace- and indent-cleaned,
applied against xonotic-v0.7.0 and rebased

Patch description for chat:
- Added (in the code for the chat) the support for modifiers
- Removed the "signed int chat_mode" thing and replaced it with an enum (generally speaking enums allow fast jump tables in switches and the code is easier to update)
- TAB completes nicks even if you're completing them from within a substring
- Ins mode (overwriting mode) by pressing INS on the keyboard (using modifier ins)
- now CTRL+{left|right}ARROW moves the cursor between words (using modifier ctrl)
- removed the exception for the commandmode, now all works as in say/say_team
- cursor changed to match those used in the console (square = ins, arrow = std)
- Support for the right/left arrow buttons and the home/end buttons.
- Support for del and backspace.
- Edit the text in-place.