Prepare for 0.1.5
Manually squash Widgy's first two migrations

This pair of migrations created and then removed a bunch of stuff in
Widgy that depended on Mezzanine. Removing each create/delete pair
allows migrating Widgy without Mezzanine.

Reviewed-by: Rocky Meza <rocky@fusionbox.com>
Reviewed-by: Antoine Catton <acatton@fusionbox.com>
(cherry picked from commit e3c9961892d17dac6f5ee6b7aa04c84a8cfef5ca)
Drop target collision detection

Instead of using the pointer_event_catcher to activate drop targets,
activate the drop target closest to the mouse that overlaps the dragged
element.

As an optimization, only drop targets visible in the viewport are
checked for overlap. The list of visible drop targets is refreshed on
scroll.

(cherry picked from commit 21bf13fb0ca475f2b7bbb557bdb1e36b8a59250c)
__str__ can't return None

Reviewed-By: Antoine Catton <acatton@fusionbox.com>
(cherry picked from commit ede08dbc3242e5bd94a698ab3a033b67c137f31a)
User delete querying nonexistent reviewqueue

A widgy project was searching for user-related review queue objects when an
admin attempted to delete said user. Thus, the site was attempting to query a
database tab le that did not exist.

Reorganizing the review queue imports within the widgy-mezzanine admin file so
that they are not called unless review queue is in INSTALLED_APPS fixed the
problem

(cherry picked from commit e54854e42053c95ac4b0d80a480aea9d5fb5044d)
Fix multi-table inheritance with LinkFields

The fields LinkFields adds were getting added twice when inheriting from
a model with a LinkField. LinkField tries to prevent this by check if
the fields are already there, but it only checked local_fields. It needs
to check all model fields, including inherited fields.

164ea5f00b3db switched from using get_all_field_names to local_fields,
because get_all_field_names loads the appcache which can cause a
circular import. This commit uses get_fields_with_model, which does not
load the appcache, so it should be ok.

(cherry picked from commit 4964243f7a3a03c4eb43453c1ed0371fc61c3e81)
Release 0.1.5
Prepare for 0.1.6