[WIP] Python bindings

[AlexanderFabisch]

In case this is interesting for anyone: we implemented Python bindings for base-types for a prototype in the project InFuse. If this should go to master, there are still some things that have to be done:

• make dependencies optional in manifest.xml and add them to a package-set
• integrate setup in main CMakeLists.txt
• compatibility to Python 2
• implement Python bindings for the rest of the types

I would like to hear your opinion about this.

An example of how it can be used (more can be found in the unit tests):

imu = basetypes.IMUSensors()
imu.time = basetypes.Time.now()
if imu.time.is_null():
    raise Exception("beeep")
imu.acc.x = 1.0
imu.gyro.x = 2.0
imu.mag.x = 3.0

@Rauldg