Improve handling of HCS missing messages

[steven-sheehy]

Detailed description:

• Change missing message logic from flatMapSequential() to concatMap() since former would run inner flux concurrently then order at the end, causing race conditions with state of TopicContext
• Moved missing messages to top level so it could take advantage of the filtering for duplicates. This helped in dev when sequence numbers and timestamps didn't match or were duplicated
• Re-wrote the missing message test to be more accurate using mocks
• Change CircleCI Maven logging to not show download transfer progress
• Bump version of Maven and Maven Wrapper

Which issue(s) this PR fixes:
Fixes #505

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated