Reorganize netconf.git features

We have five sets of features:

• features-netconf-connector
• features-netconf
• features-netconf-testing
• features-restconf
• features-yanglib

At the end of the day, OpenDaylight project guidelines call for at most three sets:

• features-netconf
• features-netconf-experimental
• features-netconf-testing

i.e. top-level projects should not have their feature repositories fragmented more than that, as it leads to incomprehensible trees (as is the case here).