[FIX] Further improve signed & encrypted rule applier. [#645 state:fixed]

- Rules are now only applied once for each encrypted & signed message.
  In case a message is encrypted it is still evaluated until its once
  decrypted. After that no longer
- The message ids are recorded in a defaults file.
Merge branch 'dev' of https://github.com/GPGTools/GPGMail into dev