ENH:Add retrieval of earliest date to data manager

The data manager will fetch whichever the earliest known date is in the
database.
TST: Add tests for getEarliestDate method
ENH: Add GUI elements for earliest known date

This required the interface structure to change a little big.

In summary the major changes are:

- All results are now displayed on screen using a gray color instead of
  a black color.
- The summary view uses the full window.
- There's a label that indicates what the earliest known date is.

Additionally the necessary logic has been added to show a message of "no
collected" data when the earliest date is (NULL).
DOC: Fix typos and update screenshot