Works around a bug in Android 7, fixed in 7.1.

Attention: This factors out a DnsModule to be able to make actual
non-Tor DNS lookups for testing.

This now also handles the case where an RSS blog is deleted via the blog
deletion option and not the feed management.

This was preventing introduction messages from getting ACKed.
The introduction tests were modified to check for this.

Signed-off-by: goapunk <noobie@goapunks.net>

Evidently this way of nagging myself to write tests doesn't work.

Also fixed a bug with settings namespaces.

* Remove distinction between "shared with" and "shared by"
* Show all contacts a blog is shared with
* Show online status of contacts in sharing screen

* Add a string label argument to CryptoComponent#hash()
* Convert DoubleDigest from implementing MessageDigest
  to implementing org.spongycastle.crypto.Digest
  (we need to keep DoubleDigest for FortunaGenerator)
* Convert all other uses of MessageDigest to CryptoComponent#hash()
* Remove CryptoComponent#getMessageDigest(), MessageDigest and DigestWrapper