BUG: Loading DICOM files with non-Siemens extensions fails

[bennyrowland]

The suspect.image.load_dicom_volume() function only handles DICOM files with extensions of .ima or .dcm, failing for the Philips approach of no extension and the GE extension of .img. The most obvious solution would be to use the extension of the first DICOM file passed to the function, and try loading all files with a matching extension in the folder.

[bennyrowland]

Fixed by #131