Create a Python 3 client build

[DominicOram]

As a instrument scientist I would like to confirm that my scripts work under python 3. As such I would like a Python 3 release that I can test them against. This ticket is to create and deploy a Python 3 client on all the instruments. The client will consist of:

• genie python
• the IBEX client
• we will also deploy a static INSTETC for texting as mentioend in All instruments: multiple IOC stalls #5323

As this is not the release that will be run in the next cycle it doesn't need to be thoroughly tested.

Acceptance Criteria

• All instruments have the latest version of the client with Python 3
• INSTETC updated

[DominicOram]

Whilst doing this we need to make a decision as to whether to update NICOS, see #5351

[DominicOram]

Also deploy this

[DominicOram]

Depends on

• Make Scan Library Python 3 compatible #5404
• Python 3: Implement new import mechanism #5262
• Scans in Shared Python Scripts: Replace populate #5401
• GUI/Scripting: config change and block names #4136 (note that this may mean that we need to release some blockserver mods as part of this ticket)

[John-Holt-Tessella]

It may also need a custom deploy script

[Tom-Willemsen]

Text to add to email to instrument scientists after deployment:

As part of the migration to Python 3, we have changed the mechanism by which instrument scripts are imported into the inst module. Existing functions should be unaffected by this change, but new functions may need to be added to C:\Instrument\Settings\config\<inst name>\Python\inst\__init__.py before they are available as part of the inst module. See https://github.com/ISISComputingGroup/ibex_user_manual/wiki/Python-3#changes-with-instrument-scripts-due-to-python-3 for further details about this change.