Remove 'created_by' from trees and plots

This field isn't really useful in OTM2 since the audit system will
automatically record an INSERT whenever a new audited object is created.
Add PIL so that the API can resize images and create thumbnails
Merge pull request #87 from ahinz/topic/remove-created-by

Remove 'created_by' from trees and plots
Merge pull request #88 from ahinz/fix/add-pil

Add PIL for API access
Refactor tests to multiple files

Previously all tests were hanging out in tests.py and it was topping
nearly 1700 lines and sort of disorganized.

This commit pulls them out with the following general structure:

__init__ : generic utility functions
audit    : tests related to auditing, pending and automatic rep
models   : a catch-all for generic model test
search   : tests for filter parsing and searching
views    : tests for views

As OTM2 grows we may have to revisit these files but for the moment it
seems fine.
Merge pull request #89 from ahinz/topic/reorg-tests

Refactor tests to multiple files
Merge remote-tracking branch 'upstream/master' into topic/add_unicode_methods

Conflicts:
	opentreemap/treemap/tests.py