Make multirecipientnotifications module the default one

[Robert Lyon]

When this module was added it was still somewhat unpolished so we made it an optional module.

One could either use multirecipient notifications or the existing notifications inbox.

Now as we arrive at 15.10 the multirecipient notifications module now the preferred one to use so we need to make it the default for all.

If one installs a new site it is the default but may not be if you upgrade from earlier versions

We fix this by:

1) Adding some code to htdocs/lib/db/upgrade.php to force the module to install and/or be made active

2) Add public static function can_be_disabled() { return false; } to the module

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/5870

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/5870
Committed: https://git.mahara.org/mahara/mahara/commit/24c957e2952dd21d2dd5ffcb5b50dd60f2e9a615
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit 24c957e2952dd21d2dd5ffcb5b50dd60f2e9a615
Author: Robert Lyon <email address hidden>
Date: Wed Jan 6 09:11:32 2016 +1300

Bug 1497065: Making the multirecipient notifications the default plugin

As this is the preferred plugin for notifications now

Change-Id: I6ca49c863bb1cd9a8f3da891ebe2ab187c3d0a1e
Signed-off-by: Robert Lyon <email address hidden>