Fixed issue with unexpectedly truncated files

* Functions to read intan data would throw an error if a file was
unexpectedly truncated (i.e. in the middle of a sample).  This will now
result in a warning instead of an error.
* Updated ViewRecordings to use images instead of lines for waveforms.
Speed is improved by ~10x.
* Added AddSimpleCustToWF to add simple clust information to WF files.
These will now appear in ViewRecordings.