add mavensmate.destroy to main's deactivate

need to tear down the MM instance created
remove existing panel items from panel

if these aren’t removed they will show back up when reactivating in the
same session.
unsubscribes from subscribed events
fixes bug where mm activated with no file open
tear down all items that were created

renames function to destroy
destroys the panel and sets it to null
unsubscribes from any subscribed events
nulls out local server

TODO: still needs to tear down local server
Merge branch 'fix-deactivation-errors'