Rather than passing a pointer to a waitgroup into task.Start(..)
functions, handle the waitgroup.Done() at the callsite.
This makes waitgroup handling local to its definition rather than it
being spread out over multiple files. Tasks now simply execute, and
the policy of waiting on them is handled by the caller.
* Implement parallel scanning and generation, and combined scanning/preview/sprite generation.
* Added UI component for preview/sprite generation during scan, and configurable number of parallel tasks.
* Add v050 changelog entry
