This patch allows the dataroot/metadata/*.xml file to be named after
the idp rather than the Mahara institution.

Also added
- A select dropdown so that institution can pick existing auth to be
paired to
- Upgrade to rename the dataroot/metadata/*.xml file
- Check to stop being able to add blank metadata field
- An alert for user when updating metadata if other institutions are also being effected
- Delete the metadata if deleted institution is only one using it

behatnotneeded

Change-Id: Ie3f5cdc523404b1081352ede67aab591e79b6dbb
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>