Poll and prepare queued Downloads #38

[patrick-austin]

Branched from #39 due to those test failures breaking the tests added as part of this PR.

• Add run.properties setting for the maximum number queued jobs to schedule concurrently
• After existing updateStatuses check, startQueuedDownloads up to the limit above - and RESTORING Downloads
• Refactor existing query in updateStatuses for clarity
• Re-enabled StatusCheckTest in pom.xml
• Removed references to em in StatusCheckTest and use the downloadRepository instead, like the other tests
  • Mostly this did not require changes to any test logic, just the utility functions, but did alter updates to Downloads in the tests to either create with those values in the first place or explicitly create new Downloads
• Tests in StatusCheckTest now use finally to remove Downloads created for the test, as failure in one test meant bad data caused subsequent tests to fail
• Changes to how the dummy Downloads are created to support arbitrary preparedIds and statuses, for testing the new functions
• Whitespace changes caused by auto-formatting my changes (tried to limit this to only functions relevant to this change)

Closes #38