Preserve filters when switching between interactive and plain text mode

Created by: attfarhan

We can now use the query parser to detect filters properly in plain text mode. Therefore, we can use it to correctly identify filters when switching from plain text to interactive mode.

In this PR, we allow interactive mode to parse filters from the q= parameter in order to maintain queries when switching from plain text mode. On the search results page, we always parse the filter filter URL parameters (repo=, file=), so that we can read the full query in the URL, regardless of which query parameters are used, in both modes.