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"? :)
This conditional is iterating through the all the inline widgets in the current document to determine if it needs to close or open, right?  Two things come up. We could break out the logic to show/hide in two separate functions.  Then have a toggle function that figures out if the inline widget should be shown/hidden.  The second part is that we could have an object to quick look up any widget that have been already added to determine if we need to show/hide (add/remove) the inline widget.