Another sanity check for Waylit events

Should hopefully prevent someone you're not at war with from causing
siege events when they're sieging third parties in provinces you
control.
Death cause is now execution instead of battle
Hopefully fix silly execution bug

Siege winners probably shouldn't execute people they're trying to
install on a throne.
Requires capital for siege events

This should prevent silliness related to the game warping you to
besieged locations in your demesne, even if they're halfway across the
map or some other nonsense.
Updated Changelog
Merge pull request #228 from thefinestsieve/beta

Various Waylit updates