- Groupchats now support XEP-0313 Message Archive Management (MAM)!
- This uses the history stored in the sqlite database, as implemented in the
previous commits.
- The QUERY-ARCHIVE megafunction builds up a SQL query to get stuff out of the
database, in accordance with provided MAM + RSM parameters.
- Notably, various hacks are in here that need to be fixed.
- IQ 'set's are now processed, which means we needed to add a stub impl of
Schrödinger's Chat so people don't drop out of MUCs all of a sudden.
(Well, it just responds to every ping indiscriminately...)
- Oh also the new presence subscription stuff from earlier is borked.
