Removed all dependencies to rtt and ocl in catkin_package()

* Packages that want to use RTT always have to call find_package(OROCOS-RTT ...).
* Catkin does not respect the LIBRARY_DIRS for rtt and ocl correctly when using DEPENDS, so this will not work anyway. See https://github.com/ros/catkin/issues/535.

The only option to make that work is to create a new package that calls `find_package(OROCOS-RTT ...` and optionally also includes the `UseOrocosRTT.cmake` script in one of its `CFG_EXTRAS` files and appends the RTT libraries to its packagename_LIBRARIES variable. This could also be integrated in rtt_ros directly.

This would allow catkin users to write very simple cmake files like this:
```
find_package(catkin REQUIRED COMPONENTS rtt_ros)
include_directories(${catkin_INCLUDE_DIRECTORIES})
orocos_component(foo ...)
target_link_libraries(foo ${catkin_LIBRARIES})
```