Verify old password is set in receiver preferences page

Refactoring of old password new password checking to reduce code duplication.
This fixes: https://github.com/globaleaks/GlobaLeaks/issues/76
Improve SHA Hash visualization.

* Makes sure the hash is displayed only if the server has already generated it.
* Hide link on receiver
* Will expand the field when hovering over it and select all when clicking on it.
Fixes: https://github.com/globaleaks/GlobaLeaks/issues/54
Merge branch 'master' of github.com:globaleaks/GLClient

* 'master' of github.com:globaleaks/GLClient:
  GLBackend and GLClient aligned to permit SMTPS and SMTP/TLS configuration