useorocos: maintain a list of exported targets and include directories in orocos_generate_package

This lists are used if orocos_use_package is called for a package within the same workspace
instead of invoking pkg-config. This allows users to generate and use packages within the same workspace.

Signed-off-by: Johannes Meyer <johannes@intermodalics.eu>
UseOrocos: adding pkg-config path for catkin workspaces which have yet to be source'd