Connects to #210. Search user experience enhancement.

[jimmyzhen]

Key Changes:

• Use the unique metadata in the top-level search response (e.g. gene symbol, protein id, metabolite) to disable the search filters (e.g. tissue, assay) that have no matches in the returned DEA results. This change applies to the DEA search and Gene-centric View pages.
• Display a more helpful message to users when selected search filters return no matches in the search results. This change applies to the DEA search, Gene-centric View, and Browse Data pages.
• Fixed uncaught UI behavior when user clicks on the radio buttons of either Gene or Protein ID after a top-level search. Now the click event reset top level search results. This change applies to the DEA search page only.

[jyu-sm]

LGTM.