Allow asset admin styles to be used in 'Choose another file' dialogue of UploadField

I've added thumbnails to the 'Choose another file' dialogue, this style change allows for that gridfield to be styled the same way with compact rows
Reflect changes in scss file
Behat: Save draft notifications have changed
Behat: Adding page publishing scenarios #616
Behat: Type case in step definition
Behat: Adding user help scenario #607
Behat: New feature "Edit site wide title and tagline" #619
Behat: Fixed indentation (no functional changes)

Using tabs consistently
Behat: Removed unnecessary access-user-help.feature

It doesn't add much value in terms of testing
(can't see how we'd ever mess up the "Help" menu entry),
and it relies on the availability of an external resource
(userhelp.ss.org), making the tests more brittle.

It also breaks the feature following this one, because
somehow Behat doesn't reset the browser session, so
subsequent logins fail because a login still exists.
Merge pull request #761 from jonom/patch-1

FIX #527 : Add Thumbnails to 'Choose another file' dialogue
API SiteTree->validURLSegment() prioritizes extension votes

Tri-state, use NULL to ignore the extension result
Using new CMSForm class to allow for validation errors in CMS

This class allows deferring handling of responses to the parent
controller's response negotiator implementation.
FIX #651 Broken redirection after creating new folder in assets
ENHANCEMENT: allow sites to override meta generator tag
Merge pull request #765 from jthomerson/enhancement_3.1_allow_disabling_generator_meta_tag

ENHANCEMENT: allow sites to override meta generator tag
Fixed spelling mistake in SilverStripeNavigator

Thanks to Donald Rogers for pointing it out
ErrorPageTest: Reset env state

Otherwise SapphireTest will complain, see 0da70dafa457564a6adb02140ffeb5dd01f3a982
Merge remote-tracking branch 'origin/3.0' into 3.1
Fix AssetAdmin::$allowed_actions
Merge pull request #778 from silverstripe/pulls/allowed_actions-deny

Fix AssetAdmin::$allowed_actions