A PlayerAttachment to deal with multiple capitals.
It controls when the attached player loses PU's due to capitol loss.
The Value is the minumum number of capitols that must be held to avoid PU loss.
<option name="retainCapitalNumber" value="2"/>
If a player has no playerAttachment, then it defaults to "X",
where "X" = total number of capitals
(ie: you lose your money if a single capital is captured)
Can be used with "retainCapitalProduceNumber", which sets the number of capitals needed to gain and spend.