Rebase from 'upstream'
Fix pc.in template
Add cmake find_package config

Thanks for urdfdom package for examples.
Add cmake rules for pymavlink installation (v2).

Use external script. (as catkin).
Some code from catkin build system used to fix installation process.
Revert "Add cmake rules for pymavlink installation (v2)."

This reverts commit 76c8eb58d18019db7572e87f0fa7dd8b39b2cd09.
Revert "Add cmake find_package config"

This reverts commit 233827865b68f9534ecc3fc8c01c6c504e2e7291.
Revert "Fix pc.in template"

This reverts commit 40a1a07b6427dd3519b6386b6913eac6091d441a.
Rebase from 'upstream'