Review server upgrade and password provider pages

This PR addresses two critical tickets for 5.0.0-beta2: https://trac.openmicroscopy.org.uk/ome/ticket/11787 and http://trac.openmicroscopy.org.uk/ome/ticket/11770

The server upgrade page on the sysadmin section should now:
- include a top-level warning about the new password provider with a  link to the relevant configuration section 
- show the exact DB upgrade commands when upgrading from either 5.0.0-beta1 or 4.4.9
- add a note about the need to reset the JVM memory settings after upgrade
The 5.0.0-beta1 page about the no-upgrade from 4.4 is removed and the server upgrade page is added to the what's new page.

In addition to this documentation PR, a matrix job has been set up [OMERO-upgrade-develop](http://hudson.openmicroscopy.org.uk/job/OMERO-upgrade-develop) which tests most aspects of the upgrade as listed on the server upgrade page:
- fire up a previous server
- download the new binaries, update the DB
- perform the optimisation steps
- restarts the upgrade server with the upgrade server
- test the dump restore and restart the old server
Some obvious next steps for this upgrade job are:
- fill the DB with some basic components (user, group, images, annotations…)
- test script upgrades