Remove organisation option and toggle on login

[ZIJ]

Users currently need to specify digger-organisation: 'digger' in digger.yml, and there is also a toggle at the bottom left on the login page. There is however nothing that the users can do with organisations in the Community Edition, it only adds clutter and confusion. Also the value of the org on the login screen does not always match the one in the workflow file.

Mo: we have this annoying thing where the orgnaisation name which appears in the bottom-left of the screen of users isn’t what they should be specifying in the digger wokflow file. in screenshot we see <company_name> visible in their screen but their actual org name was <github_user_name> so we need to address this somehow, even a quick and dirty way just to make the whole thing self service

We should make this org thing completely invisible to the user. it's our internal dealings, there is no reason why user should be specifying the org or even be aware that the concept of "organisation" exists - unless they are on the enterprise plan.

That means:

• remove the option
• remove the selector
• always have default org (say "digger") to keep things working