Python 3: Make systems run in python 3 that need to

[John-Holt-Tessella]

Systems that should be running under python 3 should now be switched to that:

If pydev doesn't work spin new tickets and decide on priority

Requires #5241 to be merged before reviewing/merging. (Fixes to matplotlib backend)

Acceptance Criteria

• Genie_python is running in python 3
• Gui scripting perspective is launched so that it runs python3
• Nicos is launched to run python 3
• Basic smoke testing - run each command in genie_python once
• disable unnneeded py2 tests (if any)

[RaiBishal]

• Nicos is launched to run python 3

This is being implemented in this ticket #4887

[Alistair-McGann-Tessella]

PRs:
GUI: ISISComputingGroup/ibex_gui#1066
Upgrade script: ISISComputingGroup/ibex_utils#57
Genie python: https://github.com/ISISComputingGroup/genie_python/pull/228
EPICS: https://github.com/ISISComputingGroup/EPICS/pull/204