Add first use screen

[monkeydom]

Should be used to configure what needs to be configured. E.g. at least:

• main user account
• smtp stuff
• domain
• storage options

[monkeydom]

To get a basic idea a look at the gogs first run screen might be of interest:

[monkeydom]

In our current deploy setup, a lot of those happen in docker container environment settings. So it'll be more likely less complete. Currently I'm thinking:

• main admin username/password
• minimal instance settings
  • allow non-admins to create networks
  • allow sign-up