Make tag-search page into a better default topic landing page

[davidmegginson]

Every HDX tag is a potential topic landing page (as we found with Ruby on the weekend), e.g. https://data.hdx.rwlabs.org/dataset?tags=health for datasets with the tag "health"

A few low-effort changes could improve the usability of those pages considerably, so that the community can easily cluster around tags/topics without our creating a custom page every time. The following would apply only when a search is for a single tag and nothing else:

• [ ] change the content of the title element from "Search for a Dataset - Humanitarian Data Exchange" to something like "Topic: 'health' - Humanitarian Data Exchange" or "Datasets about 'health' - Humanitarian Data Exchange" -- as with #1912, this will bring about a major usability improvement for SEO, social sharing, and bookmarking with very little effort.
• [ ] change the content of the h2 heading element from "All Data" to something similar to the above (e.g. "Topic: 'health'").
• [ ] start with the search filter closed by default, so that it doesn't fill most of the available screen space
• [ ] optionally add a generic redirect from /topics/XXX to /dataset?tags=XXX (that way, we could have had /topics/ruby on the weekend without intervention from @teodorescuserban)

[teodorescuserban]

I can enable this on my side whenever you want.

[cjhendrix]

Have to figure out how this fits in with the browse page. Going to leave it in the backlog for now.

[davidmegginson]

Due to my miscommunication, the /topic/XXX -> /dataset?tags=XXX redirect does exist now, in stealth mode. Example: https://data.hdx.rwlabs.org/topic/gender

Note that this is a client-side redirect (the user sees the new URL in her browser address bar), not a server-side redirect like https://data.hdx.rwlabs.org/ebola ; I suggest leaving it as it is for now, since it doesn't affect anything on the site, and it's available for rapid use if needed.

[cjhendrix]

Moving back to backlog.