Fix file link recognition in HtmlEditorField.js

The new file_link format ([file_link,id=\d+]) uses a comma which was not reflected in the regex.
Use create() to instantiate Member_GroupSet on Member::Groups()

Keeps it consistent with how HasManyList and ManyManyList are
instantiated in DataObject.
FIX Environment file finder logic

Fixing the logic that searches for environment files so that warnings
due to open_basedir are suppressed and both the 'realdir' and the server
path are spidered for the environment file.
API Full-width HTMLEditorField by default
Merge pull request #1956 from chillu/pulls/htmleditorfield-stacked

Show HTMLEditorField in full width by default
Merge pull request #1936 from mikg0/patch-1

Fix file link recognition in HtmlEditorField.js
Merge pull request #1972 from dhensby/environment-conf-patch

FIX #1866 Environment file finder logic
Fix priority of Member->getHtmlEditorConfigForCMS() (silverstripe/silverstripe-cms#728)