If a relationship isn't defined, it should not be removed. Only if a
relationship is change to a null relationship, should it be removed.
Also fixed the maxctrl test suite to verify that both it and the REST API
tests pass.
The data of the relationship should be set to null to delete the
relationship. Conceptually it is different from setting it to an empty
relationship but in practice both lead to the same end result.
Updated tests to use correct relationships and added test cases for
detection of invalid relationships.
As the REST API is a part of the core, it is more appropriate for the
tests to reside there as well. Further refactoring of the testing needs to
be done to allow multiple components to use the same framework but with
different tests.
All resoures now use the `state` member to describe their internal
state. This includes servers, services and monitors. This means that the
`status` keyword can be reserved for something else and it can be removed
until it is needed again.
Changed the module maturity field to `maturity` to better describe its
purpose.
The PATCH method should now be used instead the PUT method to update
resources. As PUT request bodies should represent complete resources, the
use of PUT to update resources is no longer supported.
Altered tests to use PATCH instead of PUT for updating resources.
