Migrate search database from Python -> Go

[orblivion]

See the description of the associated milestone for some technical background.

• This task will be for migrating the search database interactions from the Python server to the Go server. Look for anything that says search_db_path. Move it along with the associated sql statements to Go. Feel free to pull in whatever surrounding code that's straightforward enough to move to Go along with the sql. So long as it's well organized on the Go side.

• Expose whatever you move to Go as internal endpoints and call them from Python, deleting the replaced code.

You could look at the bookmark database access stuff (separate sqlite file) under go/ for some reference, though it's still in progress as of this writing.

• Please add tests and stuff as well of course. However, I would not take the time to write tests for the internal http handler functions as such, since http tests are annoying and we'll be stripping those handlers away soon anyway. But everything else, go ahead and test.