ADD: test files for troubleshooting and validation

These are all the required files for creating a raw object.
-sns.txt is the sensor locations for KIT-NYU system.
-test.elp is the digitizer laser points from Polhemus.
-test.hsp is the digitizer head shape from Polhemus.
-test.sqd is the datafile acquired from the KIT-NYU system.
-test_Ykgw.mat is a mat file containing the data extracted using the
Yokogawa matlab toolkit. This is to check that the proper data is being
extracted.
-test_marker.txt is the marker coil position within the MEG.