[lint addons] Don't error on missing dependencies

Closes #2376
[xml mode] Fix indentation after 'context grabber'

Closes #2374
[xml mode] Fix parsing of quote-less attribute values

Issue #2373
[bidi demo] Fix html highlighting in demo
[css mode] Add nonStandardPropertyKeywords list

And style them differently from unknown properties.

Issue #2356
[vim] Fix 'mark to move to first nonwhitespace
[vim] Implement gstar and ghash