Make rubble non-decaying by default.

Explicitly specify that the rubble placed on death is decaying.
This breaks quite a few mods, then again the fix is a simple sed command.
Run within your mod root directory:
sed -i 's,>rubble/,>decay|rubble/,' find simulation/templates -name '*.xml'

For fields you can just edit the few templates manually and specify decay_60 instead.

Reviewed By: fatherbushido
Differential Revision: https://code.wildfiregames.com/D938