Implements a cleanear retrieve, handles duplicates cleanly

Made some coverage model changes and updates the retriever logic to
safely retrieve duplicate values and unorder complex coverage datasets.
Updates the DAP handler and adds thorough test(s)

- Updates DAP handler to use get_value_dictionary
- Verifies ArrayType and Complex Coverage support
- Verifies visualization support
Adds skiptest for test_ccov_visualization if PyDAP is disabled
Updates submodules

Previous HEAD position was 8aae5b4... Merge pull request #69 from
lukecampbell/fillvals-r2
HEAD is now at 6aa1def... Merge pull request #71 from
lukecampbell/loclrng-qc-r2

Previous HEAD position was 63a06af... Release 2.0
HEAD is now at c339b71... Merge pull request #113 from
lukecampbell/timeseries-r2
Merge pull request #1359 from lukecampbell/replay-work-r2

Better retrieve support for data management