* Do not remove localstorage items while looping
While looping over all the browser storage items by index, the items
should not be removed because removing alters the index positions. The
item following the removed one will be skipped by the loop.
Instead, accumulate a list of keys to remove and remove them after the
loop.
* Implement full delete support for browser storage plugin
Before, deletes only worked for tiddlers which are only present in the
localstorage. Now deleted tiddlers are marked in localstorage using an
empty string value.
At startup, the localstorage tiddlers with empty strings will be deleted
from the wiki if they are still present. If they are already gone from
the wiki, then the blank localstorage entry will be deleted.
* Document drawbacks to using '[all[]]' and provide an alternative
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