Update HtmlTextView
Don't include SDK info in AndroidManifest.xml

It's set in the gradle config now.
Change log tag to "APG"
Fix Key serialization

The data returned by key.getEncoded() cannot be decoded on its
own by PGPObjectFactory. That'd require a key ring and with that
a master key.

The new serialization serializes the Key object and allows restoring
it accurately without creating a key ring as a workaround.

In PgpKeyOperation this requires adjusting the public key, as that
one is queried with isMasterKey(), and it is considered a master key
if subSigs == null. To avoid this, subSigs is initialized with an
empty ArrayList, resulting in a true subkey.
Remove unused imports
Make KeyRing.decode() deal with lack of key rings
Lift the plus button of user id sections
Update bc