Replace the current filters with user queries

The current user queries can be quite limiting (no negative check, no OR, no checking of anything but the result itself, no regular expressions on tests/machines/tags, ...). Rather than having to write scripts directly (like proposed in #47 (closed)), we should instead use the lovely query language we introduced earlier (thanks @karolkro!). The query language would become the central tool, which would be lovely!

The transition should not be difficult because we already have a way to convert filters to the equivalent query. However, we will have the following changes to make:

• The new filter will just be a human description and a (multiline) query: convertion of current queries can happen through a migration and using the already-existing equivalent query
• The distinction between covered/matched will need to be done automatically: We will need to visit the AST of the query and replace any query on stdout, stderr, dmesg, or status with always-matching ones.
• We need to beef up the autocompletion and editing (thanks to @emersion for his initial work)
• We need to change the way we import results: we should first import results, then query the DB for the covered results, then matched ones.

@karolkro, @bretdavi: any feedback on this?