Unit Testing Setup for new Python API

[dokempf]

In order to properly test our code, we need example data that is as cheap as possible. The demos used for regression testing are not fit for this purpose, as they are too big.

There should be at least fixtures for the following objects:

• scanner -> singlescanner
• scene
• survey
• singlescanner
• multiscanner
• platform
• tripod + other platform prototypes

These fixtures are to be used solely if we do not care about the specifics of the object.