Add more configuration settings

Currently this agent can configure the following settings:

• Zones, Users and Servers as basic objects
• Servers can be trusted giving full access to everything or untrusted, not allowing to update zones on other servers
• Each zone has a single key giving full read and write access to a single zone

Additionally i now want to have the following options:

• Restricted keys: keys which may be only readonly, or only be allowed to update some records in a zone
• Services: basically the same as a restricted key, but shared beween multiple zones
• comments: knot supports comments in the configuration data, we can use it to add web links for objects