settings refactoring

[renothing]

there are so many global options for gitea. and the variables grew up more and more. it's so boring for upgrading, user have to check every config variable before upgrade. maybe it's better to make a distinction. we can make two part:

• 1: readonly: like database settings, ssh server settings, domains
• 2: writeable: like smtp, security etc...

and only keep part 1 in config file or read from enviroments, write part2 into database with default values.
then we can keep the docker image clearly and upgrading safe than before.

What do you think?

[lafriks]

I would like to see writeable settings moved to configurable storage (file, databse, etc)

[lunny]

I think we already start moving part of configurations to database.