General UI drag changes

Changes to UI drag behaviour:
- Multi-touch drag support
- Combo press touch support -- you get id mask of pressed buttons + number of buttons + the average of their positions

Line edit now has a numeric mode:
- Supports setting a precision for # of decimal points formatting.
- Supports drag editing; can set increment amount, increment smoothing, button mask to activate the drag.
- E_TEXTFINISHED is sent when LineEdit is defocused (press enter, escape, press away from it / finishing a drag).

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*The scripting isn't set up properly*, in particular I got stuck when trying to describe return values for HashMaps. It would also be good if the editor was also updated to reflect the numeric mode in the attributes editor.

One extra thing that would make drag editing with LineEdit better is to overcome the screen-boundary. Currently if you do turn it on in the editor, you'll notice dragging near the edge of the window will limit drag editing usefulness.