Feature/remove checkbox "badge" before sending

This feature adds a check-box in the "Send" tab which needs to be unchecked ("removed" like a saftey badge) in order to enable the "Send" button. This shall prevent accidentally sending a messages without having checked the content, the sender and the recipient.

In the settings you can set the behavior of the checkbox. By default, there will be no badge not to annoy users who don't need this. Thereby the feature is unobtrusive.

In future versions the user should be able to set the behavior separately for each Identity (e.g. no badge for the general chan, but badge for personal address)