Tb montage enh

Adds montage option to edf and brainvision modules to provide standard import of electrode points.
Adds fiducials to the montage.
Organization of transformation functions into the transformation module.
the `path=` parameter is unnecessary here. `read_montage` is clever: when a full path is specified, it will use it, otherwise it will look in the `mne/channels/data/montages` folder.

It would also be nice to be able to specify an instance of `Montage` here to be more flexible. Only use the `read_montage` is a string was specified.