BEL sensor layouts and coordinates

[ephathaway]

Currently, one can only write sensor layouts and coordinates XMLs if they exist as resources in the mffpy lib. As we develop new EEG recording devices that utilize the MFF format, we should add their sensor layout and coordinate XML files as resources, so that we can write these types of MFFs.

Devices in the works:

WISP
Geodesic Head Web 130
Geodesic Head Web 280