Issue 202 disappearing sharerooms

Fixes #202.

Fetches of public share rooms that fail, but have succeeded since the share room was being remembered, will no longer knock the share room off of the list.

Instead, the entry will be displayed with a grayed out "≈" aproximately-equals sign and the share-id / room-key.

Tapping on the entry (or selecting the longpress menu "open") will reattempt the fetch, and visit the share room if the fetch succeeds.  If the fetch still fails, a toast will notify the user and the list will remain the same.

Finally, the details screen presents the abbreviated set of available details, plus "Successful fetch pending" as a kind of status.

Though new public share room entries still cannot be succesfully added while offline, being offline will no longer clear the list of already-remembered ones.