EPIC 3.1: QGIS GEOSYS Processing Algorithm

[AndreLester]

Expectation: As a QGIS Processing toolbox user, I would like be able to incorporate the retrieval and analysis of GEOSYS products into my workflows.

Acceptance Criteria:

• Given the GEOSYS plugin is installed and my credentials are set in the options dialog, when
  I open the QGIS Processing toollbox, then the GEOSYS plugin will be available.
• Given that I am using the GEOSYS Processing Algorithm, when I define the request criteria
  in the algorithm then the algorithm should successfully return the dataset requested.
• Given that a date is requested, when the user presses OK, then the most recent coverage
  before the chosen date will be retrieved.
• Given that the GEOSYS algorithm may retrieve more than one coverage, when the user
  presses OK, then the algorithm will merge the retrieved products as a single virtual raster and
  add that raster to the QGIS map canvas.
• Given that a sensor is selected, when the user presses OK, then only coverages for that
  sensor will be returned.
• Given that a polygon layer is selected, when the user presses OK, then the algorithm will
  iteratively search GEOSYS for each polygon by passing the WKT string representation of the
  polygon.