Plugin mechanism for sensors

[alex-sever-h]

Instead of hard-coding the type of environmental or light sensors, make a plugin mechanism where just having a binding created in a folder automatically loads the specified sensor.

[BabyCakes13]

In #23 I have started the restructure to support this.

[BabyCakes13]

Merging #23 does not close this issue, it was a start for implementing the project plugin style. We still have improvements to do to get to fix this. One of which is finding a way not to store sensor types at the core off the project (snapshot at this time):

class Motion(SensorType):
TYPE = 'Motion'

Adding motion required change of core code because the types are hardcoded in the core code. We should make this also plugin adapted.