Improve Bugsplat dialog

[Hofknecht]

our bugsplat dialog looks like this:

• There should be option 'Close' or 'Restart' (currently it is always restart, theoretically it is possible to stay in a loop)
• exception should be shown in textbox, in case there is no default email app
• maybe also directly a link to create it on github
• better would be if default email app not needed
• maybe consider extra textbox then for user feedback

[Hofknecht]

we added a cancel here to prevent hanging in a endless loop: #360