[Demo] Manage several cities

[Lecrapouille]

• Creation/suppession/selection.
• 1 application == 1 city.
• 2 applications == 2 neighbouring cities ?
• When creating a road crossing to cities we have to popup to accept or refuse the road. Improve virtual bool allowSegmentAcross(City& owner, City& neighbor, SegmentProposal const&proposal) to make it asynchronous. How to manage when the neighbor city make several minutes to accept. Option 1: Create a dummy road blocking the creation of other units. Option2: once accepted erase units along the road.