Better search focus management

[cloverich]

Current state (as of #217) is: focus search box produces a dropdown with suggestions (no typeahead support yet). After deleting or creating a search tag, the typeahead (re)pops open.

Escape closes the dropdown, and is basically a required action.

I think instead do this:

• cmd+f to focus search
• adding and removing tag closes popup, de-focuses input
• but typing after refocuses input and shows dropdown