There is no need for NeochatConnection to depend on ThreePIdModel and also this means it's not in memory when not needed.
Also a little cleanup to make sure only a single job can run at a time.
Since _ls is now deprecated this is removed in favour of L1, I've also taken the oportunity to replace QStringLiteral and QLatin1String with their shortened form while we're at it.
There are also a few instances where the string literal type has been switch, the general rule being to use the one that matches the function type or value being compared to avoid conversions.
Turns out trying to manage pointers in the model is a bad idea so only save eventId in MessageContentModel, events pointers will now only be obtained temporarily then discarded to avoid both creating additional copies of the event in the model and potential sources of crashes.
This also creates a basic unit test that we can add to going forward.