Add feedback plugin to MaxScale

It would be very useful to know what kind of configurations are used with MaxScale as that would allow is to focus on the features that are used and to deprecate and remove the features that are not.

MaxScale should have feedback functionality that basically would mean that it at startup would upload the used configuration (with sensitive information removed) to some server. In betas this functionality would be enabled by default, in the release version it would be disabled by default.

Further, MaxGUI could have [button] using which the configuration of MaxScale and the servers could be uploaded explicitly.