Secure passwords from 3rd party clipboards in OSX

[andyfase]

Hi

gopass does not support securely copying passwords into the OSX clipboard. Thats because under the hood it its using pbcopy which does not support adding the attributeorg.nspasteboard.ConcealedType see and this issue

To work around this in the Alfred Workflow I suggest we should use the in-built Alfred clipboard functionality (which does support org.nspasteboard.ConcealedType) hence passwords will not be picked up by any 3rd party clipboard tools on OSX (including Alfred itself)

This PR alters the workflow adding steps to:

1. Remove use of gopass-c flag for using the clipboard
2. Adds step to copy password to clipboard using Alfred with "transient" option set
3. Adds steps to simulate clipboard auto-clearing after 45 seconds as per gopass

[woopstar]

Any updates to this?