Add a Filter for MTH Leaders in MNG

[Daza99]

On the Leaders screen in MNG it would be very handy to have a filter in the "Key Info" menu MTH Leader, these are a feat if an MTH you are a shareholder with and a good standing will offer a leader for you to take. Later on you have an opportunity to form an Alliance with that MTH and they want you to fill some of your leadership roles with their leaders. The alliance opens up cheaper contracts, but I presume this will only be so if you do your part with giving their leaders roles in your regime. So being able to filter them in your Reserve Pool would be handy.