Allow demo data generators to be interruptable.
Added option to switch progress bar to indeterminate mode.
Made the status of a device more verbose:

- allow to determine whether a device is cancelled, acquiring or
  ready. Allows UI to be more explicit about what to expect.
Usability improvement:

- make the client more explicit about the various states a device
  can be in. For example, when cancelling an ongoing acquisition,
  the device might not immediately be ready to restart an acquisition,
  hence we need more detailed information about what state a device
  is in.
Several bugfixes:

- fixed a NPE when recapturing on a SUMP device due to a missing
  configuration;
- made the SumpAcquisitionDataBuilder a little more robust and
  easier to maintain;
- fixed a potential performance bottleneck when flusing an input
  stream with *lots* of data (for example when cancelling on a
  Pipistrello).