Device 'type' obsolete

[qgeissmann]

The type of device (SM vs SD) used seem to be obsolete now. We have a much more generic and fuzzy conception of ethoscopes.

On the back end, this is mainly sorted by #8. Control thread still has some "device type" information though.
On the front end/user interface, we will need to get rid of the hardcoded distinction between SD and SM at some point.

[qgeissmann]

I have started to remove this from the backend. nod type is only 'sd'. I know it is used in the front end, so until we remove it from there, I will keep the "type" field in ControlThread._info

[qgeissmann]

@pepelisu I am going to try removing the concept of type from the front-end now.

[qgeissmann]

@pepelisu I did refactor the front-end quite a bit:

• Removed quite a few lines of code related to 'device_type'.
• Renamed 'sm' to 'ethoscope' everywhere (e.g. http://127.0.0.1:8000/ethoscope/...).
• Also removed some of the obsolete code to increase readability.