Simplified Special:MWOAuthManageMyGrants listings

* Improved form error messages in Special:MWOAuthManageMyGrants.
* Improved some UI messages.
* Also fixed a fatal in getWikiIdName().
* Also fixed a few annoying form bugs.

Change-Id: Ic7ae9103909df0f8c51e18d5bbe9f684ecd9ef64
Merge "Simplified Special:MWOAuthManageMyGrants listings"