[wip/ros-realtime-tools] Fix some glitches

- Wrap long lines in DESCR
- Fix HOMEPAGE (actually drop it, since the default in
  meta-pkgs/ros-base/Makefile.common is fine).
- Shorten ROS_COMMENT to ~60 chars
- Drop useless dependency on tinyxml
- Fix typos in depend.mk
- Add a ros>=hydro requirement in the Makefile, since this package is not
  available in groovy. This is currently a show stopper, because robotpkg
  supports only groovy with PREFER.ros=robotpkg, so this package cannot build
  ATM.