[FEATURE] Provide manual trigger for clearing expired tiles

[JaffaKetchup]

What do you want implemented?

cachedValidDuration allows for the automatic replacing of tiles when they become to old, in some browsing modes. However, it would be nice to be able to manually trigger a removal of all tiles that are older than a certain age.

This was originally requested by @eidolonFIRE in #119.

What other alternatives are available?

Pre-v6 it was possible to easily access the underlying IO storage. However, now that Isar is in use, this is much more difficult (although still possible).

Can you provide any other information?

No response

Severity

Annoying: Currently have to use workarounds