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When the set of tabs used fluctuate, the memory of which number
belongs to which chat becomes difficult to work with. Non-numbers
can be used to navigate tabs with `/win`, however, it is difficult
to know which letters are required to select a certain tab.

This option introduces a display mode for tab names where only the
unique prefix of the tab name is shown, saving space and providing
with a minimal string which can be used with `/win`.

All this crap is very brittle due to circular deps and python handling
them badly. This appears to be fixing some stuff, at the very least.

This is sed, so cleanup of imports (which can now be grouped together)
is not done yet.

Reduce the number of calls to config.get whenever possible. Yields a
performance improvement of at least 10% for the basic use case of
"receiving a message in the current tab". Logging stuff isn’t free
either, even when the call should be a no-op, so we should try to make
the debug log less verbose.