use targetted mimeType for VIEW catch-all to avoid catching Contacts types

GPG's Contacts integration uses the app-specific type:
vnd.android.cursor.item/vnd.info.guardianproject.gpg.encryptfileto
FileHandlerActivity should not catch that type, instead ContactIntentRouter
should be the exclusive handler of it.

refs #1454
handle receiving images from galleries as best we can.

Its not a great situation, since the main Google Gallery will show files
that only exist in your online store as a regular image.  But when you try
to share them with a SEND Intent, GPG cannot access the data...

#refs 1454