adding boost-python support for cv-bridge

The ROS package cv_bridge needs the Boost.Python library. This
commit adds a bbappend file that includes Boost.Python in the
boost recipe using PACKAGECONFIG.
This PACKAGECONFIG for boost is available since commit
TODO
in the openembeddded-core repository [1].

[1] TODO
cv-bridge: initial commit
image-transport-plugins: initial recipes from Andreas Hildisch