Drop melodic + kinetic support for master branch

[rhaschke]

Alternative to #57: Due to incompatible moveit_msgs, the master branch cannot compile on Kinetic and Melodic anymore.

[davetcoleman]

@rhaschke thinking about this further, this master branch should still work on Kinetic & Melodic because moveit_msgs is included in the rosinstall file to be built from source. Right?

[rhaschke]

Of course, building everything, i.e. moveit_msgs, MoveIt, and the tutorial from source, should still work on Kinetic and Melodic. However, to use the tutorial, users shouldn't be required to build this huge workspace from source. Hence, I suggest to drop Kinetic and Melodic support on master. Thus, the master branch, just serves as a development branch for a future Noetic release.