Feature Request: Per-photo indication of storage status

[nep2ner]

It is currently unclear whether a particular photo is stored in cloud-only or in cloud + local storage. I suggest two modifications to make this more clear:

1. Create an "On Device" option in the side menu (maybe directly below "Gallery") that lists all of the photos that exist in Stringle's local encrypted database.
2. Add a status indicator (some type of down arrow maybe?), much like the existing “not-yet-synced” indicator, that informs the user if a particular file is available offline or not.

This feature is important because user's will likely want to retain photos of things like IDs on their device at all times so that they can access them when internet isn't available.