ARC4 compilation script improvements for CASIM/SOCRATES

[cemac-ccs]

Made modifications to ARC4 compilation script so that:

1. The keywords file is linked from the working versions fcm-make/keyword-monc.cfg file to the users ~/.metomi/fcm/keyword.cfg file, meaning the keywords file does not have to be populated manually
2. The mosrs password is cached so that branches and revisions can be checked out
3. a dialogue is given to the user to allow them to choose compiler options

This should remove much of the initial barrier to use for new users on arc4. Similar work has been done on the archer2 compatibility branch

[leifdenby]

This looks cool @cemac-ccs 😄 really nice.

How are you thinking this will work if someone wants to modify their copy of CASIM/SOCRATES? Or we saying they shouldn't use this compile script in that case?

[cemac-ccs]

If using a locally modified copy of Casim/Socrates, the user would need to change the references in the compilation script to an appropriate fcm-make/<tool>_local.cfg file and put their branch path in this config file.
Probably worth it to add instructions for this to the doc - I'll write up text for it in the other PR