Check into validity checker (Android)

[rachelhamlin]

Problem

Also reported by Trail of Bits:

I couldn’t find a file validity checker. This is important when you are using external storage. The permissions in the Android manifest indicate that you are using external storage.

Implementation

The point of this issue is to investigate whether this exists or not.

Acceptance Criteria

Comment on whether we have a file validity checker on Android. If no, please create separate issue for follow-up.

[churik]

Obsolete and will be re-considered in the redesigned app.