Alpha: WikiGrok in sidebar

* Introduce a new flag $wgMFEnableWikiGrokInSidebar which should be set
  to true to enable this feature;
* Enable for logged in users or anons if $wgMFEnableWikiGrokForAnons is
  set to true;
* Update the spinner code in WikiGrokDialogB.
* You can test it by appending the following query parameters and hash
  to the page URL: ?mobileaction=alpha&wikidataid=Q3784220#wikigrokversion=c

Change-Id: I0af2cbea22a0b43393e6dd73bdec75bdc753c949
Merge "Alpha: WikiGrok in sidebar"