have the app create the initial admin user:
* if the db has not yet been set up
* if there are not users
* if the config value for Init.CreateAdmin is True
* if the admin password is not empty
default username, email values can be seen in modules/user/const.go
this entails a couple of breaking changes due to schema evolution. once
the schema is stabilised, backward compatibility promise will be given.
* update config struct and accompanying scructs
* update tests
* update exampleConfig.dhall
* update local dev environment (devenv)
* make settings reflect the config schema changes
* make use of some settings/config updates
* let the settings struct be the single source of truth
* rm app fields that are covered by settings
* pass around a pointer to settings instead of config
* consolidate config+flags into settings on start-up
* update tests
* rm empty settings.go file
fixes#4
