Fixed #19139 -- Made OpenLayersWidget follow GeoModelAdmin's modifiable attribute

Thanks Tim Graham for the review.
Prevented Attribute error in GDAL objects deletion
Fixed #13843 -- Prevented AttributeError during geometry objects deletion
Fixed #17101 -- Integrated django-secure and added check --deploy option

Thanks Carl Meyer for django-secure and for reviewing.

Thanks also to Zach Borboa, Erik Romijn, Collin Anderson, and
Jorge Carleitao for reviews.
Added ops team to roles.txt.
Fixed #23483 -- Prevented ImproperlyConfigured with dotted app names

Made sure the app labels stay unique for the AppConfigStubs, so
migrations wouldn't fail if two dotted app names has the same last part
(e.g. django.contrib.auth and vendor.auth)
Fixed #23484 -- Add comment in AppConfigStub clarifying app name vs app label.
Added 1.7.1 release notes for refs #23483.
Forwardported 1.4.16 release notes.
Fixed #23461 -- Added EMAIL_TIMEOUT setting
Fixed #23466 -- Removed seconds from all locale time output formats.
Fixed #23397 -- Stripped whitespace from base64 during chunking

This insures the actual base64 content has a length a multiple of 4.
Also added a test case for the failure.
Factorized create_index_sql expression
Fixed broken link in 1.7 release notes.
Fixed occasional selenium test failure on Jenkins with Chrome 36+.

Previously find_element_by_id('id_password') on the next line failed with
NoSuchElementException and selenium.page_source was
<html xmlns="http://www.w3.org/1999/xhtml"><head></head><body></body></html>.

Possibly related: https://code.google.com/p/selenium/issues/detail?id=1969.
Move my bio to "Past team members" section whilst I'm inactive.
Fixed #23474 -- Schema migrations can inadvertently destroy data

Changed MigrationExecutor.migration_plan to not unapply migrations
that it shouldn't be unapplying by passing the subsequent migration
of `target` to MigrationGraphy.backwards_plan, rather than `target`.