UI/RNA: added pixel and percentage units to some properties

Reviewed By: brecht

Differential Revision: http://developer.blender.org/D99
Code cleanup: float<>double promotion
This is a very WIP patch that implements Scintilla as the back end of the Text Editor.

So far ~90% of editing functionality is implemented
(loading, saving, undo, syntax highlighting, search/replace, etc).

As per Campbell's suggestion, it is implemented as a build option
(WITH_BF_SCINTILLA) so that if/when this code is in master,
it can be tested and we can always fall back to the default implementation if needed.

There is only Scons support currently and I've only compiled the code with Win64/Mingw.
Again this is a WIP, meaning there are many known bugs,
comments to myself, printf()s, and can crash Blender. By posting this patch I'm hoping to:

- Get a general yay/nay on if this seems reasonable to continue implementing
- Make sure it compiles on other systems
- Generate interest in development (especially due to my lack of knowledge of DNA, UTF8, opengl, etc)

I'm not looking for a detailed review, just high level suggestions/opinions.
There is still a lot to do to get it completely functional and up to the same level as the current code.