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
7568bfdd114597956a1da68746f207ec7f93a48d
in the openembeddded-core repository [1].

[1] http://cgit.openembedded.org/openembedded-core/commit/?id=7568bfdd114597956a1da68746f207ec7f93a48d
cv-bridge: initial commit
image-transport-plugins: initial recipes from Andreas Hildisch
README: document dependencies on recent commits
packagegroup-ros-world: adding new image-transport recipes
Merge pull request #145 from bulwahn/image_transport_plugins

Initial recipes for image_transport_plugins (resolves #136)