Rebase from 'upstream'
Fix root cmake for building as ros 3-rd party library (v2)

With fixed invocation of mavgen.
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.
Add install rule for package.xml
Add libdir hack from urdfdom.
Add supported dialests list to find_package() script.