Allows to save media in a different path than the state store.
This adds a "last_access" field to the SQLite implementation, to prepare
for future work on a media retention policy.
This removes the IndexedDB media cache implementation, because as far as
I know it is currently unused, and I have no idea how to implement
efficiently the planned media retention policy with a key-value store.
Closes#1810.
- [x] Public API changes documented in changelogs (optional)
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Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>