Implemented all Admin functionalities for the Servers.

- Admins now interact with REST Controllers, as will the mod
	- Could not integrate a shell for the admin operations (spring-shell or integrated shell)
- Implemented a master key (created at each application start) for admin operations
- Using an in-memory H2 database for development
- Implemented List, Create, Rename, Change Key and Delete Server.
- Controllers return OperationResult objects in JSON format.