This PR fixes some things about crash handling:
- when the terminate handler is called, immediately set it back to the
original one, so can't make a recursion if the crash-handling code fails
- Only save projects if the crash occured after Imhex finished startup
- do not update the project location when saving the crash backup file:
this will remove problems when `EventAbnormalTermination` is called
before `crashCallback()`
I also added a bit more documentation
In order to do this I add to make some other additions :
- Add a warning popup (TODO, maybe add some icons to differentiate
error/warning popups in a future PR ?)
- create showError() and showWarning() functions, as helpers to show a
message both to the logs and as a popup
