templates: cmake_modules provides FindEigen, so explicitly depend on it. Fix #27.

Also change order of `find_package(..)` statements to reflect this and
update dependency checking in pkg generator script to allow for different
run and build depends (`cmake_modules` is only a `build_depend`).
templates: remove superfluous link_directories(). Fix #23.
templates: include planning group name in plugin desc install rule. Fix #28.
scripts: any change to run or build depends should trigger manifest updating.
Eigen is not actually a dependency anymore, so remove build_dep on cmake_modules.
Merge pull request #29 from gavanderhoorn/for_master_issue23_27_28

Fixes for 23, 27 and 28