Add VIIRS SCF processing capability and merge with current IMS_proc

[yuanxue2870]

This is the first step towards adding VIIRS DA capability in the original (vector formatted) offline land-only DA workflow. Note: in the land component model (tile formatted) offline land-only DA workflow. More edits will be required and will be housed in a different branch/repo.

Revisions in this issue/PR include:

1. added VIIRS processing unit;
2. merged VIIRS processing unit with IMS processing one;
3. added VIIRS super-ob percentage threshold as a parameter in the namelist file;
4. added a new VIIRS test case, and separated from previous IMS test cases.