Consider other feature modalities apart from Acc. and RSSI

[perellonieto]

The current examples only consider accelerometer and RSSI values. However, if the library wants to be general and more useful to other research groups it would be convenient to thinkg about other modalities and see if they fit in the current framework, or how this should be modified.

Some examples of modalities that may be non-trivial to be added are RGB video data, or silouhetes.