markov: Finish up chain database implementation

Markov now uses a sqlite3 database instead of flat JSON files. This
should significantly speed up saving time, plus reduce the amount of RAM
that it uses. Saving and loading large JSON files was very slow and
caused issues with other plugins, especially when messages were
received. Additionally, in order to save RAM, a cache was used and
periodically flushed when not used, adding some complications to the
implementation. This has all been removed since things get committed on
the fly with the database implementation. The main trade-off we have to
make is the disk space used by the database. This is OK though, because
disk space is cheap while RAM is not.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tools/markov_import.py

@@ -40,7 +40,7 @@ async def main():
                     name = mat["name"]
                     message = mat["message"].strip()
                     if name != server_config.nick and message and message[0] != "!":
-                        plugin.add(channel, name, message)
+                        plugin.add(channel, name, message, commit=False)
     await plugin.save()