Made a setting for using native or custom scrollbars
fixed hack so switching between native and custom works correctly
Add native scroll bars preference to default preferences.json.  Also add command and menu option to toggle the preference
Merge pull request #438 from TheKiteEatingTree/scrollbars

Toggle Native Scroll Bars
Turn relative common.js requires into absolute ones so that loading the
same module with different relative paths results in the same module.
Update submodules
Added treehugger to zed/lib for sandbox, includes a parser for
JavaScript and Python (currently). May have to factor this out later.
Python parser is used for an improved Python mode (currently reports
parse errors with semantic analysis in the works).
Work in preparation for preferences UI.
Added new preference UI