Rewrite search caching to allow sharing search links [$15 awarded]

[nijel]

Currently the search results are cached and after this the URL is not longer shareable. This is quite unpleasant for users which sometimes send links to show particular translation.

The caching has to stay in order to have consistent view when translating (once you filter not translated strings, you want to be able to navigate through it even if you have translated something meanwhile).

Currently it works:

• If the URL contains search_id, it is directly fetched from session cache and used.
• If the URL contains search parameters, new search is performed and stored in session cache, further only the search_id is used in the URLs.

We can most likely identify the session cache directly by parameters thus avoid need to exposing some internals in the URL.