Add "stations" locations

[raplima]

Is your feature request related to a problem? Please describe.
Feedback from the first workshop. The program should be able to make use of "stations" vector files (points?) as that is hard evidence of the lythology at that location.

Describe the solution you'd like
The program should be able to read a point vector file (or isolated polygons?) and use those stations as training samples.

Additional context
This would help with what I consider to be one of the major drawbacks of the current methodology. As of now, the training points are randomly selected from the mapped geology and there is no control on their location. Such strategy can lead to highly biased training samples.