This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
https://meta.discourse.org/t/search-logs-page/73281/11?u=techapj
This commit adds following features:
- support for tracking click through to user, tag and category
- new filter for search type (header, full page)
This commit also removes "most viewed topic" field from search logs page because we are now tracking multiple click through entities, so topic is not a special entity anymore. This also improves query perf. The query now takes `20.5ms` to runs, as opposed to `655.9ms` previously.
