Adding in Siemens TWIX Read

- Add in twix read files from Philipp Ehses
- Add .dat to DiscernDataType (and separate from sdat).
- most new code in SiemensTwixRead.mat
Merge branch 'master' of https://github.com/cjohnevans/Gannet2.0

Conflicts:
	GannetLoad.m
	Spectral_Registration.m