Add management for configs

This PR enable the ability to manage configuration settings via adding a mongoose schema and Linz will convert this to a document and store it against linzconfigs collections.

To-do:
- [x] Linz to load config files and create documents in linzconfigs collection
- [x] Add router control for accessing the list of config in the Admin UI
- [x] Add navigation item to access the list of configs
- [x] Editing capability for configs via Admin UI
- [x] Overview display for config
- [x] Ability to reset config to default values
While you're at it, would you mind adding the same for models?