Added support for reverse order:

- added functionality to provide the samples in reverse order as
  used in some SUMP-compatible devices.
Major refactoring in SUMP device:

- cleanup and rename classes to use Sump prefix as LogicSniffer
  is less generic;
- simplified & speed up the conversion of raw bytes into sample data
  by using only a single pass conversion. Thanks to Magnus K. for his
  great explanations on the semantics of the returned data.
Some cleanups.