Add "Non aggression pact"

[MasterSon-git]

Add diplomatic action to propose "Non aggression pact" to another player.

• start an event like tranfer money weher you can choose length of treaty 5/10/15/20 years
• needs to be accepted by target player
• if rejected next proposal to this country is blocked for 2 years
• results in a truce between both countries

reason for this is to allow players representing their off game treaties

[MasterSon-git]

duplicate of #314