Adds deactivate to unbind vim-mode event listeners

This PR addresses the issues of event duplication in #230 by removing the event listeners created by the `registerCommands` method in `VimState`.

Since jQuery event namespaces are `.vim-mode` suffixes instead of `vim-mode:` prefixes, I would like to advocate the removal of the `vim-mode:` prefix on event handlers and their associated trigger calls.  Currently, the namespace doesn't interfere with the use of the prefix, but it is very redundant to have both, and as near as I can tell, the intent behind the prefix was to act as a namespace.

I can either make the removal part of this PR or submit a supplemental PR that handles the prefix removal, if it is determined that is the way to proceed.