Find current institution based on current theme for a user

[Robert Lyon]

If a user is in multiple institutions then they can choose which theme to view the site in via the User account settings.

This is saved as [theme]/[institution] in the database

When they go to a page which has an institution selector it defaults to the first institution they are in rather than the institution they are viewing the site as.

For example the Progress bar institution selector.

It would be good if we can select the institution based on the institution value in the account theme preference.

And then default to the current way we do this if that value is not set.

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/7826

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/7826
Committed: https://git.mahara.org/mahara/mahara/commit/4de78659452db8bab73264901d976c1ab0983610
Submitter: Aaron Wells (<email address hidden>)
Branch: master

commit 4de78659452db8bab73264901d976c1ab0983610
Author: Antonella De Chiara <email address hidden>
Date: Fri Jun 16 11:01:10 2017 +1200

Bug 1698242: Get current instittuion via usr_account_preference theme value

behatnotneeded

Change-Id: Ie14a090eaacbdabf621d366109c5082107eba50a
Signed-off-by: Robert Lyon <email address hidden>