* Remove koreader-sync credentials from config
These are supposed to be set via the login/logout mutations and are not meant to be set manually by the user. Thus, they are not really settings and do not belong to the config
* Reduce log levels of KoreaderSyncService
* Cleanup graphql setting mutation
* Validate values read from config
* Generate server-reference.conf files from ServerConfig
* Remove unnecessary enum value handling in config value update
Commit df0078b725 introduced the usage of config4k, which handles enums automatically. Thus, this handling is outdated and not needed anymore
* Generate gql SettingsType from ServerConfig
* Extract settings backup logic
* Generate settings backup files
* Move "group" arg to second position
To make it easier to detect and have it at the same position consistently for all settings.
* Remove setting generation from compilation
* Extract setting generation code into new module
* Extract pure setting generation code into new module
* Remove generated settings files from src tree
* Force each setting to set a default value
