JSP: Welcome page

Depends on #266 (closed)

Include number of datasets under "number of accessions"

1. Rename "ACCESSION MAP" to “Quick overview”
2. Add “XXX Datasets” with link to Catalog/datasets page at https://catalog.genesys-pgr.org

Changes to the top navigation bar

1. Remove "Home"
2. Add Datasets menu in header:
   Order: About Genesys, Browse, Datasets, Countries, Institutes, My List
   Link to https://catalog.genesys-pgr.org/datasets

Update Controller and welcome page JSP.