netcontrol/api.py: Add first use case devices()

In order not to change the previous behaviour of the application, it still
takes the network interface as a parameter.

Desirably, we wouldn't want this and by default the application should try
to scan all the networks, and a user shouldn't even have to know what a
network interface is.
netcontrol/api.py: Add methods existing in NetController

And substitute any call to these methods in NetController with the new
ones.
core/netcontroller.py: Remove unused file

Now that we have the API defined in netcontrol/api.py and the methods
are implemented there, there's no use for this file anymore.
Merge branch 'complete-moving-api'