Make `this` refer to module object when calling sandbox API

May fix problems with #128
Fixes #132
Fixes #114 with basic implementation of continuous completion
Initially switched off by default so we can iron out the bugs and corner
cases. Be sure to update your Ace build by running `make`.
Remove context bar, now no longer in existence, preference toggling
Clicking the path in the window title now opens up the Goto UI.
Tweaked continuous completion (#114) slightly by selecting the first completion
by default.
Push font size config into the sandbox.
Add brand new configuration options to the sandbox.
Merge pull request #140 from robru/sandbox_config_int

Allow Sandbox to control integer preferences.