Enhancement: better plist text highlighting

[gregneagle]

the plist/ace editor is using "generic" XML highlighting; even better would be plist-specific highlighting.

For comparison -- TextMate's XML highlighting:

And TextMate's plist highlighting:

Though the difference is not dramatic, it does highlight keys differently than values, which I think is helpful.

[gregneagle]

Documentation here on ace syntax highlighting:
https://ace.c9.io/#higlighter