Change implementation of data type detection

Remove the code to skip a file if a waveform channel is encountered in processing.detect_data_type, fixing #160 (closed). In order to compensate for the waveform records that now have to be processed, a faster algorithm is used to get channels from an MSeed file.

Also, processing.get_data_type_from_file returns None for any non-MSeed and non-RT130 files.

Updates tests for processing.get_data_type_from_file to be more comprehensive.