Review EPICS-extensions content

[Tom-Willemsen]

In https://github.com/ISISComputingGroup/EPICS-extensions/tree/master/src we have lots of things which are questionable at best:

• medm
• edm
• php_epics
• 3 copies of gateways (but the one we actually use is in a different repo, https://github.com/isiscomputinggroup/epics-gateway )
• 3 copies of msi
• A copy of dbVerbose of 2013 vintage

As a developer I would like to not have unused code in our repos, remove any items on the above list that are no longer required

[FreddieAkeroyd]

If it is not being built by https://github.com/ISISComputingGroup/EPICS-extensions/blob/master/src/Makefile we probably don't need it