Improve local storage purging

[BridgeAR]

Feature request

Description

As a user, I want to clean up my local storage in a useful manner so that it does not fill up.

Acceptance criteria

• Add timestamps to all saved data
• If data is used again, update the timestamp with the last used time
• Check timestamps while loading the page. If data has not been used for more than 6 month, suggest to prune that data (open a window asking the user about it).
• If the local storage fills up (exceeding a specific amount of kb [TBD]) ask the user to clean up grouped data (check for usage frequencies. Data is mostly used throughout a couple of days and then there's a break in-between. Those grouped times should be auto detected and a useful date should be suggested for deleting data to free enough space (~50% of the considered maximum amount).