Metadata - review functionality and integration tests

[andreasrs]

Not sure if the current metadata implementation is correct.
Currently basic dicts of changes are supported, and the integration tests simply verifies that Imbo returns http 200 and expected response bodies upon metaata changes. Not sure if this is the intended behaviour from server.

[andreasrs]

@matslindh do you have any input on this? I guess quite a lot has happened on the server since this was created as well.

[matslindh]

I'm not too familiar with the metadata API yet, but I'm going to dive into this and update the library API to have a sensible way of handling it (probably by modeling it after the PHP client).