Add a mission objectives GUI panel
Add end game dialog
Make necessary changes to existing maps
Remove inconsistencies w.r.t the Surrender order

* Surrendering is now possible even in maps that do not use
  ConquestVictoryConditions.
* The Surrender button is greyed out instead of hidden when it cannot be
  used.
Add some Media functions to new Lua API
Convert gdi01 to new Lua