Fixed two major bugs in libpit related functionality:

- Partitions were being excluded from flashing (and UI) if the block-count
  was zero. Instead this is now done using a new IsFlashable() method
  which checks if the partition name is not blank.
- PitData::Pack() was packing the partition name where it should have been
  packing the "flash filename". This resulted in incorrect PIT files being
  flashed to the device.
Minor command line output changes - No functional changes.
For devices that support variable packet size - decreased sequence size from 100 MiB to 30 MiB.
Fixed bug in Heimdall Frontend where "resume" wasn't being checked when it should have been.