Local layout syntax highlight foundation

[Lorenzo Bertini]

Hello list,

attached is a patch that adds a syntax highlighter to the local layout 
QTextEdit that supports some very basic LyX syntax. I remember someone 
asking for this, but nonetheless it can be useful.

I've encountered some problems and I would appreciate your help:

1. I can't find how to put files I've added to git inside a patch to 
send, so I have attached the two files, both go in src/frontend/qt. Sorry :)
2. LyXHighlighter differs a lot from LaTeXHighlighter: doesn't rely on 
regex as much. I was wondering if a merge could be possible, considering 
local layout can include Latex bits.
3. Generic regex based on position or keyword recognition. Which one?
4. Syntax keywords are hardcoded right now (I only added a few 
properties because it's tedious work and there's probably a better way). 
Is there a place where I can find all keywords LyX uses in a layout?

Thanks a lot in advance

Lorenzo
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