Set up OCDP-specific Home and About pages

The navigation bar link to the OC Data Portal now leads to a home
page similar to that for Dash itself. Within the OCDP, searches
and links to About pages take users to OCDP-specific resources.
All OCDC-specific pages share CSS styling.

Searches within the general geographic interface now also return
results within that interface, as do the metadata links within the
result listings.