Configurable theme not displaying correctly after upgrade

This also happened when an upgrade took place from 16.10 to 17.10.

At minimum we should have a message on "Admin home" saying something along the lines of:

The following institutions use the configurable theme. Please re-save the institution settings page to apply the styles properly again.
- Institution A
- Institution K
- Institution Z

The institutions should be linked to their settings page.

We have something similar for when an institution had SAML setup prior to Mahara 16.04 and then was upgraded but didn't have proper SAML data stored in the institution settings but still only on the server.

Patch for "master" branch: https://reviews.mahara.org/8783

Environment tested: Master
Browser tested: Chrome

-------------------------------------
Manual Test Script
-------------------------------------

Preconditions:

1. Mahara 16.04 Stable is installed with an empty database
2. Institution A exists with the following
----- a. Theme = Configurable Theme
----- b. Registration allowed = Yes
----- c. Confirm registration = No
3. Institution B exists with the following
----- a. Theme = Raw
----- b. Registration allowed = Yes
----- c. Confirm registration = No
4. SIte admin user exists with the following:
----- a. Inst Admin of Institution A
----- b. Inst Admin of Institution B

Test Script - User upgrades Mahara from 16.04 to 18.04

1. User performs the upgrade from 16.04 to 18.04
2. Confirm that when the user logs in for the first tiem that the following message is displayed ✔
------------------
Your latest upgrade may have stopped your configurable themes displaying correctly. To display the themes properly again (and remove this warning), please go to the settings page for each affected institution and re-save the theme by clicking "Submit". (Administration Menu -> Institutions -> Settings). The following institutions use configurable themes:
institutiona
------------------
3. Site admin browse to Institution A settings
4. reselect the configurable theme in the Themne drop down field and submit
5. Browse to the Dashboard page
6. Confirm that the Theme is now displayed correctly now with the colours of the Configurable theme settings ✔

Catalyst QA Approved ✔

Reviewed: https://reviews.mahara.org/8783
Committed: https://git.mahara.org/mahara/mahara/commit/8cac996b6eb7efbe04e9974f7eefb62ffdde2b55
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit 8cac996b6eb7efbe04e9974f7eefb62ffdde2b55
Author: Rebecca Blundell <email address hidden>
Date: Thu Apr 5 18:30:51 2018 +1200

Bug 1760732: Add warning for upgrade of configurable themes

Add 'customthemeupdate' flags for any institution to the
institution_config table if:
- the upgrade is from 16.10 or before
- and the institution is using a configurable theme

If there are institutions with 'customthemeupdate' set we add a warning
that the institution settings need to be re-saved.

Once the settings for an institution have been re-saved we clear the
flag for that institution

Steps to test:
1) Have a 16.04 version site
2) Create three institutions, two with a configurable themes
3) Checkout the patch and run upgrade
4) On clicking 'Continue' you should see the warning message
5) On going to Admin dashboard you should see message there also
6) Edit / save one of the institions
7) Confirm that institution is not listed
8) Do for the other and see warning now gone

behatnotneeded

Change-Id: I844d8e8bcb9be81a29f36cb101da1c61b41b10a9