Remove checks for options and callbacks

My understanding is that we either implement a robust and logic check for
mandatory inputs at initialisation time or we might as well not bother and let
execution fail on its own, should the inputs be lacking in some way.
Invoke callback via SortingQueue's own interface

This enables us to take advantage of its built-in error checking logic.
Move method into private section
Make variable local
Rename to `callback´
Don't use about to deprecated request mechanism
Reindent code block
Fix uneven padding
Add `chrome´ to jshint global clause
Reindent comment block
Do not accept user-specified bins
Do not keep reference to `MessageHandler´ instance
Add class for handling of messages from content scripts
Add class hint
Implement logic for saving of state
Add event handlers
Append emacs mode hints
Implement on-demand initialisation of bins controller
Remove logic responsible for bin hierarchy
Rename `bin´ to `data´