Repeating air recon missions

Added the ability to have repeating air recon missions. When in recon mode, hold down shift while selecting a tile, releasing shift will then run the mission as normal. Pressing shift+R on later turns will run all the missions you've added in this way. Missions stop whenever a unit moves or you select a new mission for it. In the future, may add the ability for aircraft based on carriers to keep the repeating mission (relative to the carrier?) when the carrier moves.

Unzip and put in your CustomAssets/Python directory. If you already have a modded CvEventManager.py you'll need to diff my changes in manually.