[PATCH] Update entities visibility at the beginning of the game

[Itms]

The territories don't explore the map anymore when the borders change. However, the territory should still be explored at the beginning of the game.

[Itms]

In 15612:

Hide changes to buildings in the fog-of-war.

To achieve this, mirage entities are created per player, to replace the real entities when these ones fall into the fog-of-war. These mirage entities are created on-the-fly, and destroyed when they get back in sight.
This depends heavily on the VisibilityChanged message added in r15508.

As a temporary adjustment, territories do not explore the map anymore when their borders change. See #2709.

Fixes #599

[Stan]

It seems it's because you removed UpdateTerritoriesLos(); ​in CCmpRangeManager.cpp in r15612 ​¶

[Itms]

I implemented this and I also added code to see entities when the "Explore Map" option is set.

[Itms]

In 15681:

Explore the map inside a player's territory border at the beginning of a game.
Also handle properly the "Explore Map" option with the new fogging system.

Fixes #2709