Fix ROS Melodic/Dashing buildfarm failures

[wxmerkt]

octovis is currently failing on the ROS Melodic and Dashing buildfarms because my previous PR accidentally omitted a required dependency (and that the fallback builds libqlviewer-qt4 in the source tree).

This PR:

• Fixes the missing dependency in octovis' package.xml (and also changes the style back to build and exec dependencies)
• Also changes the generation of CMake config files etc. to happen in the binary dir instead of in the source directory. This is required on read-only filesystems
• Adds the public link attribute for octovis

@ahornung, could you please make a patch release 1.9.2 after this PR? Thank you :-)

[ahornung]

Also changes the generation of CMake config files etc. to happen in the binary dir instead of in the source directory. This is required on read-only filesystems

Is this necessary for the build farm? If not I would treat it separately for a 1.10 release. It changes the output directory of the compiled binaries (source target).

When cloning your branch locally and compiling the complete distribution, octovis fails to link for me (cannot find liboctomap.so). No idea why it didn't occur on Travis, though.

[wxmerkt]

I will split the PR then. I am using ROS Industrial CI locally to run on a clean Docker. There it linked successfully - and mounts the source directory read-only which is why it's required.

However, neither the master branch prior to the changes nor this one finds the libqqglviewer library at runtime. There werent any linking errors.

[wxmerkt]

I've reduced this PR to only include the changes to package.xml and split out the other two commits. It doesn't work with ROS Industrial CI now, but should fix the ROS buildfarm failures.

[ahornung]

Thanks! That should do the trick to move forward, we can then tackle the read-only FS issues separately. I just released v1.9.2.

We should probably get rid of the Qt4 dependency sometime soon, and switch to Qt5 completely for octovis.

[wxmerkt]

Thank you very much @ahornung. I will make the ROS releases to fix the buildfarm.