GUI: Stop all OPIs from moving focus

[DominicOram]

As a user I generally dislike where focus goes in an OPI (see #4785, #4760, #2646). The fix in all cases has been to create a dummy button that always takes focus. This dummy button has to be the last thing in the OPI and we rely on developers manually ensuring it is the case. This is brittle, we should:

• Try and fix in CS-Studio (has probably already been looked at a bit, unlikely to yield a solution)
• Add a step in check_build.py to confirm the dummy button is still the last thing in the file.

Additionally we could get check_build.py to insert dummy button into all opis if not present. The x/y of the button must not be placed such as to extend the OPI's area, so a little thought will have to go into this. (potentially controversial, to be discussed)

[DominicOram]

After discussion with @John-Holt-Tessella and @Tom-Willemsen we agreed that inserting the dummy button is a good idea and this should be done on a git hook

[DominicOram]

Work started as part of a Friday ticket at https://github.com/ISISComputingGroup/ibex_gui/tree/Ticket4786_stop_OPIS_moving_focus. Left to do is:

• Deploy the hook locally
• Work out what the hook should do after it's modified the file (add the modified files or abort the commit?)