Add keybind and change custom inline widget to Brackets' inline widgets.

Fixes #38.

 - Changes custom inline widget to use default inline widgets
 - Ctrl/Cmd+Shift+E opens the descriptions of the errors on current line.

@peterflynn: Could you check my implementation of inline widgets to make sure I'm not doing anything "bad"? :)
I see. Good to know - I guess that means that just using `addInlineWidget()` is enough to update the data within the inline widget (if I can't find a way to update the data without closing and reopening the widget).