Rework 'Caused By' to require less clicking

[natanfudge]

Example mixin crash: https://crashy.net/E7QNOI9QXIMbPu8ehGrj
The reasoning being:

mixin exceptions are easier to read in raw format
otherwise you have to click on the caused by button 3 times to view the actual cause

Solution: show all caused by at the same time.

• The first button will say Shell Exception: XException and will represent the first exception you currently see. At the start it will be selected.

• The second button will say Caused by: YException and will be the second exception. It will be selectable and selecting it will not change what buttons are visible - it will only make it be select instead of the first button.

• If there are >=3 exceptions, the final button will say Root cause: ZException

• If there are >=4 exceptions, the buttons in-between the 2nd and final one will say third cause, fourth cause, etc

• If there is not enough space then the buttons will overflow to additional lines.

[natanfudge]

Implemented in 2.0