gnupg-for-java: expose gpgmeOpDecryptVerify as a proper Java method

Currently this will throw an Exception if the verify fails. We need to
implement gpgme_verify_result_t in Java, like GnuPGGenKeyResult.java in
order to get useful information about the verification process.

refs #1567
add methods to create PGP ASCII pattern matchers to detect ASCII contents

A .asc file can be a lot of things, so we need to look at the embedded
headers in order to see what the contents is. This will be very heavy on
large files, but since we're aiming for ease of use, I think its
worthwhile to include.  Plus, large files should be binary, not ASCII.

refs #1569 refs #1455 refs #1456
make EncryptFileActivity receive files via an Intent

This allows other internal Activities to call it to handle encrypting
files.

refs #1454
add DecryptActivity to handle decrypting anything we throw at it

Currently this only supports file:// Uris, but it is intended to handle
all Uris once we get InputStream/OutputStream support into GnuPGData.

refs #1455 refs #1456 refs #1581
REBASE add methods to create PGP ASCII pattern matchers to detect ASCII contents