Add “Swap Order” right-click menu option for marriage

[martinvanzijl]

Is your feature request related to a problem? Please describe. No easy way to reverse the order of spouses in marriage.

Describe the solution you'd like The following:

1. Right-click on a marriage.
2. Click "Swap Order".

This swaps the positions of the spouses (i.e. left spouse goes to right, and right spouse goes to left).