v0.6.1

Bugfixes:
- avoid crash with "AttributeError: 'ChoiceBox' object has no attribute 'show_error'"
  commit c189c7e257f3cb788b6953f0cf824e78f2e8eb94
- don't crash when entering invalid values in integer entries
  commit 56a96acb20d03a104142a85bb3c649771ac362bb
- don't accept invalid input
  commit 7c7de3b2e3d678b2a413853c1672ca5c210eea33
- don't quit if saving fails
  commit affc5b9cbe9522641894b81e42ebd601a3720e3f
- w and q don't ignore changes in MessageEdit and SignalEdit
  commit 8ef093cc684ffc0983d570e53d194a7f87f1573a
- close ChoiceBox even if saving has failed
  commit 8fd5108c9ba81547697e9bc81e22d3c58d498548
- detect when new messages are saved
  commit c34b8e4acbca704e082d6738c0ac742e638fb758
- handle control + C
  commit f71674fc67e3b8b1c61c37d2bd86db7a5a569d91

New features:
- added cancel button to save changes dialogues
  commit 5d10ebcea50a3238193a1dc099b10cf696e848a5