NEW: Add Thumbnails to 'Choose another file' dialogue

Very difficult to choose an image based on file name alone. Added thumbnail and reduced rows from 10 to 8 to compensate for increased height of rows with thumbnail included.
Fix: Enable delete button for users with canDelete() but no canEdit() permissions

$form->makeReadonly(); iterates over all fields/actions, disabling the 'delete' button even when the user has permission
BUG Trigger TinyMCE onChange more frequently

Periodically check for inline changes when focused,
since TinyMCE's onChange only fires on certain actions
like inserting a new paragraph, as opposed to any user input.
This also works around an issue where the "save" button
wouldn't trigger if the click is the cause of a "blur" event
after an (undetected) inline change. This "blur" causes onChange
to trigger, which will change the button markup to show "alternative" styles,
effectively cancelling the original click event.
BUG Correct relation saving in DataObject->duplicateRelations()

This caused problems when duplicate() was used in the CMS UI
to duplicate a SiteTree object. Since every object of this type
has a ParentID relation, it copied this empty relation into
new "ghost page".

See https://github.com/silverstripe/silverstripe-cms/issues/689
ENHANCEMENT: Do not attempt to run abstract test classes

There is no reason to try to run test cases of a class that is abstract.  By
skipping them we allow developers to create abstract test case classes that
have test functions in them.  This is especially helpful when someone is
testing multiple implementations of the same service interface.  Most of their
tests can be in the abstract class, and then they can create concrete test
classes for each of their implementations and inherit all of the testing that
is built into the abstract class.
ENHANCEMENT: allow overridable JS/CSS minification

This allows someone to extends Requirements_Backend and plug in their own minification
of files, including CSS minification.  It also allows them to override whether or not
the header comment is written for each file.
ENHANCEMENT: allow disabling of Versioned prepopulate_versionnumber_cache

In large sites this can take a very long time, drastically slowing down the CMS
admin.  Even though the versions will then need to be queried individually,
this is still significantly faster than loading hundreds of thousands of
version numbers in one query and populating the cache array.
Behat: New fixture notation in "manage files" tests
Behat: Support for TreeDropdownField
Behat fixture refactoring (shared factory instance)
Behat: Copy fixture identifier to "Name" or "Title" by default

This makes fixture setup less verbose, particularly for behat
tests (e.g. with "Given a page 'About Us'")
Behat: Use explicit fixtures
Behat: Backport improved dropdown step handler
Merge remote-tracking branch 'origin/3.0' into 3.1

Conflicts:
	tests/behat/features/bootstrap/SilverStripe/Framework/Test/Behaviour/CmsUiContext.php
Enhancement: replaced privete with protected in order to have MySQLDatabase class extensible
Behat: Fixed step notation
BUG Accept $limit=0 in SQLQuery->setLimit()

SQLQuery->setLimit(0, 99) should result in "SELECT ... LIMIT 0 OFFSET 1".
In fact it does "SELECT ..." without a LIMIT clause at all,
which is unexpected. This is regardless of the $offset value.
Merge pull request #2067 from chillu/pulls/sqlquery-zero-limit

BUG Accept $limit=0 in SQLQuery->setLimit()
 Ensure Cookie::get() will immediately return results.

Without this change, a call to Cookie::get() immediately after Cookie::set()
won't return the value provided.  This creates some unintuitive edge-cases,
although to date it looks like they have been worked around.

The patch doesn't have a test because our testing framework doesn't deal
with cookies well.
Merge pull request #2068 from sminnee/cookie-fix

 Ensure Cookie::get() will immediately return results.