Bugfix: prevent crash when popping view during swipe to delete

Symptom:
In the MaltAdditionViewController or HopAdditionViewController, enter
into "swipe to delete" mode.  Hit the back button.  Crash.

RCA:
There's a bug, purportedly introduced by Apple, that deallocates the
table view data source before the table view, which causes an
EXEC_BAD_ACCESS later on.

Fix:
When the view diappears, take it out of edit mode.
http://stackoverflow.com/questions/19230446/tableviewcaneditrowatindexpath-crash-when-popping-viewcontroller
Turn on zombie debugging
Refactor: OBDrawerTableViewDelegate now owns cell 'move' and 'delete' logic

This commit will facilitate work on issue #14

Previously this was implemented in both OBMaltAdditionTableViewDelegate.m
and OBHopAdditionTableViewDelegate.m.  The code was largely duplicated.
In order to do this, a new protocol was formed: OBIngredientAddition.
This protocol allows ingredients to remove themselves from recipes.  This
is a bit awkward, but causes no problems at the moment.