Include runPythonFile service

This enables to directly launch a python file within any roslaunch file

we introduced a second service next to "runCommand", called "runPythonFile" which takes a complete python script and parses it. This enables us to setup the dynamic-graph and SoT as a single include line in any of our roslaunch files. This can for example load the complete environment and is then accessible via the python_interpreter.

example:
```xml
<node name="run_command" pkg="dynamic_graph_bridge" type="run_command" ns="sot_controller" args="$(find sot_controller)/python_code/demo/demo_dynamic_velocity_damping.py" output="screen"/>
```