Change the behavior of the difficult skill level

[Skywalker13]

The difficult skill level should be more difficult.

The objects and enemies that are covered by the fog, should not appear in the map and in the statistic list (under the map). The pause button should be disabled in this mode too.

• [x] hide enemies in the fog
• [x] hide enemies in the stat (when hidden by fog)
• [x] disable stat click on enemies in the stat
• [x] disable pause button

[Skywalker13]

All done