MRG: Add verbose argument

[larsoner]

We get a ton of these messages in MNE because we use add_data:

Updating smoothing matrix, be patient..
Smoothing matrix creation, step 1
Smoothing matrix creation, step 2
Smoothing matrix creation, step 3
Smoothing matrix creation, step 4
Smoothing matrix creation, step 5
Smoothing matrix creation, step 6
Smoothing matrix creation, step 7
Smoothing matrix creation, step 8
Smoothing matrix creation, step 9
Smoothing matrix creation, step 10

This will allow us to pass verbose=False to avoid them (this process is quick enough we don't need to be informed of the progress).

[larsoner]

Travis failures are unrelated and fixed by #205