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
Hey @sandytrinh, this isn't the end of the world at all. But we had discussed the convention 'return early', so that we don't need to use else statements like this. I just think it's a little bit cleaner to read code that way. What do you think?