Fixed ThreadPool keeping standalone application alive

[littleaj]

The initializer ThreadPool had a few issues:

1. it was using user threads instead of daemon threads causing the application to wait until all user threads died.
2. it had a minimum pool size of 1 so a thread in the pool was always available, but this is just a one-shot operation.
3. it was an unnamed thread and therefore hard to find.

Fix #662.

TODO

• Test with standalone application.
• Audit use of ExecutorService and Runnable to see if there are others.
• Changes in public surface reviewed
• CHANGELOG.md updated

[dhaval24]

Looks good to me assuming you have tested all the scenarios and smoke tests are ofcourse passing :)