Improve crash screen and reporter

The crash screen and the reporter have been split up into two separate fragments and layouts, because this mess wasn't really maintainable anymore. I took care to not do other functional changes beyond the split to not introduce any new bugs. Further improvements should be easier now.

I took the liberty of also adding a crash icon to the screen. It adapts its size to the available space, so it won't show when there's not enough space. The buttons are fixed to the bottom of the screen and are always visible.

The report form is now scrollable:

Closes #1054 (closed), #1012 (closed)