REBASE FileHandlerActivity: set up as central router for incoming Intents
DecryptActivity: always write plain data to private file

This used to write out the plain file next to the encrypted file.  Since
gpg now makes it easy to VIEW a encrypted file, there is no need to decrypt
in place.  Instead always decrypt to the app's private files/ storage. This
way it won't be written out to the SD card as plain, etc.

It will then be shared to other apps via a ContentProvider.  Once we get
streams working in gnupg-for-java, then all of the actions will happen with
streams rather than files.
gnupg-for-java: reduce the keylist return to the bare minimum for speed

This makes the keylist functions return much less information, so hopefully
it will speed things up.  There should be an option for getting the full
info when its needed.

refs #1621
claim openpgp4fpr: URI scheme and launch dialog to receive from keyservers

GPG now registers to handle the 'openpgp4fpr:' URI scheme as a way to
direct OpenPGP 4 fingerprints to GPG for it to handle them.  Currently, it
prompts the user to download the key with that fingerprint from the PGP
keyservers.

openpgp4fpr:5E61C8780F86295CE17D86779F0FE587374BBE81

refs #471 closes #1594