Add starting phase and max phase to map files and Atlas

[feneur]

It should be possible to specify starting phase for each player in the map file. This should be implemented so that it's possible to set starting phase for each player separately in Atlas as well (just as well to implement that ability as well at the same time the map file support is implemented). Since it's so closely related a way to set a "highest reachable phase" should probably be implemented at the same time.

[zoot]

"Phase" is very data-dependent. How about instead doing "starting techs" and "unallowed/unavailable techs"? To set Town Phase as starting phase, you would simply set the "Town Phase" tech as a starting tech (i.e. researched from the outset of the game). To set Town Phase as max phase, you would set the "City Phase" tech as unallowed/unavailable.