send a local broadcast after key changes so consumers can update views

fixes #1486
Contacts mimeType should be specific to the action, not the included data

We incorrectly thought that the MIME Type used in the Contacts actions was
describing the data, but it is really supposed to describe the action.
So we renamed it from openpgp4fpr to encryptfileto in the gpg namespace
when calling gpg2 command-line-style, use "--trust-mode always"

We don't yet have any concept of trust management in the app yet, so set it
to "always" so we can actually encrypt to keys, etc.
handle "Encrypt File To" ContactIntent using the gpg2 command line

This is a first step to getting the full flow working. Right now, its using
the gpg2 tool in a Runtime.exec() call, then just writes out the file next
to the original file to be encrypted.  Ultimately, gpgcli should handle
incoming streams, EXTRA_TEXT, EXTRA_DATA, etc.