Config server with settings

Added setting interface (ServerSettings and ServerInternalSettings) for server to access its configuration properties.

Enabled to obtain a server property with Config.get + property settings. Replaced the previous Apache Configuration + constant string property-accessing-pattern. 
There is no need to have this validator after using Config to get the DB Location as a default value is already assigned in the legacy_db_location setting. We could have added a simple test e.g. "ShouldNotRemoveDatabaseStoreDefaultLocation" for the legacy_db_location setting to make sure no one will remove the default value by mistake. However removing the default value of the db location should never happen as that's part of the API. In one word, did not see the need to have a test.