Use victory conditions json's in Atlas

[bb]

Atlas currently hardcodes the victoryConditions in map.cpp (to create its checkboxes). This makes adding new victory conditions more work than it should. It should read all required data from the json in the public mod (like gamesetup does). This should also include the disabling and unchecking of conquest_structures{units} when conquest is checked (so we can nuke OnConquestChanged in map.cpp).

related #5075

[Stan]

In 23847:

Use victory conditions json's in Atlas

Reviewed by: @Angen

Differential Revision: ​https://code.wildfiregames.com/D2393

In P23881:

Fix Atlas crash introduced by rP23847

Reviewed by: @Angen @vladislavbelov

Differential Revision: ​https://code.wildfiregames.com/D2898