Refactoring PlacementPreview logic

[Belonit]

• General code refactoring
• Added ability to load theater-specific shapes - #642
• Translucent tags now should be set to 0\25\50\70 instead of 0\1\2\3
• Renamed tags and fixed documentation errors:
  • In AudioVisual
    • BuildingPlacementPreview.DefaultTranslucentLeve ---> PlacementPreview.Translucency
    • BuildingPlacementGrid.TranslucentLevel -------------> PlacementGrid.Translucency
  • In BuildingType
    • PlacementPreview.Show ---------------------------------> PlacementPreview
    • PlacementPreview.TranslucentLevel -------------------> PlacementPreview.Translucency
  • In ra2md.ini
    • [Phobos]->ShowBuildingPlacementPreview -------------> [Phobos]->ShowPlacementPreview

Old Documentation vs New

[github-actions[bot]]

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[Cpj636]

There is my testing feedback: All three tags in [AudioVisual] work fine. Theater-specific shapes can be specified by PlacementPreview.Shape. Theater-specific palettes can be specified by PlacementPreview.Palette. All the rest tags work as expected.

[Belonit]

The PlacementPreview.Shape tag does not currently support save\load. Need to fix