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
Deprecate Aggregate and DataObject::getComponentsQuery
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)
Adding test to prove issue with HTTP Header parsing in RestfulService

I have a header like:
X-BB-Auth: xxxx

and it is being given back to me as X-Bb-Auth - i want to prove the issue and the fix
FIX RestfulService header parsing now accepts non-title case headers
Merge pull request #2212 from dhensby/patch-3

Adding test to prove issue with HTTP Header parsing in RestfulService
Merge pull request #2202 from tractorcow/3.1-aggregate-deprecation

API Deprecate Aggregate and DataObject::getComponentsQuery
Member.lock_out_delay_mins configurable, password security docs
BehatFixtureFactory 5.3.8 compat (wrong usage of is_a())
Merge remote-tracking branch 'origin/3.0' into 3.1
DOCFIX: small typo causing linking error
Merge pull request #2214 from chillu/pulls/password-docs

Member.lock_out_delay_mins, password security docs
Typo
Merge pull request #2220 from jthomerson/pulls/small_doc_fix_1

Small typo causing linking error
Merge pull request #2224 from tractorcow/3.1-foreignkey-typo

Typo
Test allowedExtensions in UploadField, return correct HTTP status
Updated loop/if/with to be more consistent
BUG Prevent clickjacking in CMS and Security controllers (fixes #2215)