GUI TextBox

Allows the GUI to create a scrollable text box for long text that
may not all fit on the screen. Also includes code to allow the
console to wrap on spaces and other such characters instead of
wrapping in the middle of a word.

To see an example of how to add a text box to the XML, see:
https://gerrit.omnirom.org/#/c/14183/

Change-Id: Ifd139172ede290046b58ea3fe526e2e06da1d4ef