Education and better migration update

• Some textual fixes by @historyjackz
• Performance, bugfixing
• Universities #418
• Social guaranties should affect migration target #153
• Spread in time pops migrations\promotions growth. Add map showing population change (and density). Track short history of pop's promotions #425
• Add population density map #428
• Full list: Nashet/EconomicSimulation@v0.17.0...master
  Windows standalone: ES18win.zip