Settings refactor

• Greatly decreased overall verbosity of settings/config
  • New getter: mergedConfig - combines user config with instance-default config, no more need for instance.thing !== undefined ? instance.thing : user.thing
  • Settings page now automatically creates all needed computed properties with setters - no more need for optionSettingLocal and relevant watchers - only thing needed is to define settings in module.
• Replaced most trivial checkboxes with <Checkbox> component, decreasing overall verbosity in user-settings/settings templates, streamlining other checkboxes.
  • Other checkboxes are deemed non-trivial and probably will be replaced later.