Add ability to choose difficulty of campaign missions.

[simplyjames]

Currently the difficulty of the missions in the singleplayer campaign are based on your pilot rank. It would be a nice feature to choose the difficulty before a mission. Something like easy, normal, hard. Or even choosing 1-10 (basically choose the rank)

 

I like to ease myself into new aircraft but when the difficulty is automatically at 9 it makes the campaign a bit frustrating.