FIX: GridField button styling

Remove all top/bottom margins from buttons and apply to GridFieldButtonRow component. Ensure that all buttons are added to a suitable GridFieldButtonRow in ModelAdmin, SecurityAdmin and Group.
FormFields now allow setting of extra CSSClasses en masse

Each CSS class passed in to `addExtraClass` or `removeExtraClass` will be set as their own key in the `extraClasses` array

Also make `Form` consistent with `FormField`
Adding tests to `FormField` and `Form` for extra classes

Added tests that were missing from `Form` and ones for my new logic
FIX Empty Datefield with defined min or max has non-object error thrown

When submitting a Datefield with no value but with a min / max config date, the validate() function attempts to access a function on $this->valueObj (which is a non-object)
FIX: wrong class name being returned

This resulted in an error since the returned class name did not exist.
Note that this only happened when someone subclassed GridFieldDetailForm
and did not subclass GridFieldDetailForm_ItemRequest.
FIX Avoid infinite loops on ?isDev=1 and Deprecation class

If any of the functionality triggered by Director::isDev()
was causing deprecation errors, the system would go into
an infinite loop. Since the only way to cause this is the DB
checking functionality, we disable that for Deprecation.
Side effect of this change: You can't show deprecation notices
on a live site by forcing the session into dev mode.
Updated field class to use doubleborder mixin
BUG Fieldgroup styling
fixed undefined offset #2276
Minor bug fix to show link description field 

When adding a link, the description field was present, but hidden. Adjusted javascript to show the description field
FIX: pass controller as reference inside closure.

Non referenced causes segfaults on PHP <= 5.3.8 environments when opening subtrees in the CMS. Likely the cause of silverstripe-cms/issues/803.
Changelog note on form method limitations

See 14c59be85e9ec53cb2f0b3e9d0d8ce7569d913c6.
Raised by Fara Rustein of Deloitte Argentina (CVE-2013-2653).
FIX Flush on memory exhaustion and headers sent
FIX Include flushtoken when install redirects to successfullyinstalled
API Disable discontinued Google Spellcheck in TinyMCE

Replaced by browser-based spellchecking if available (Chrome, Firefox),
with instructions on how to use PSpell as an alternative.
Merge pull request #2284 from wilr/closure_this_reference_fix

FIX: pass controller as reference inside closure.
Merge pull request #2278 from jonshutt/patch-1

Minor bug fix to show link description field
Merge pull request #2277 from joernroeder/3.1

fixed undefined offset #2276
Docs: Consistent arg quoting in <% require %> (#1614)
Merge pull request #2271 from ARNHOE/3.1-twotoneborders

Updated field class to use doubleborder mixin