Make `Failed to load osu!.exe` error more user-friendly

[Lekuruu]

I think that the current error message may be unintuitive for the average user. It would be nice if the message could be changed to something more "helpful", if that makes sense.
For example: "Failed to load osu!.exe. Please ensure you have placed this executable inside of your osu! installation folder."

[Oreeeee]

I think that a better crash handler could be made in general, something similar to the one built into osu!stable. Just saying a vague error message and dumping the stacktrace into a Win32 messagebox is not user friendly at all. Maybe the stacktrace should be hidden by default, and the message should have links to support (Discord/wiki)? Should probably be made as a separate issue though.