[New Feature] Screen/Map select buildings

Description:

One of RA2/YR best features is selecting screen/map (T), but this doesn't work on buildings. The only way to group buildings now is to shift-click each one and assign them to a number like 0.

When you have lots of war factories and barracks, grouping becomes difficult. When a factory is busy releasing a unit and a new unit is ready, the next free factory will release it, so grouping is very useful to change the relay point of all factories during an assault (like somewhere closer to enemy).

Possible Implementation:

Pseudocode suggestion:

// first gather all selected building types
HashSet<Type> SelectedBuildingTypes;
foreach (Item in CurrentSelection)
{
  if (Item.IsBuilding)
    SelectedBuildingTypes.Add (Item.Type);
}

// then parse all player buildings on the map to select them
foreach (Building in Player.Buildings)
{
  if (!SelectedBuildingTypes.Contains (Building.Type))
    continue;

  if (MapSelect || ScreenSelect && Building.Visible)
    Building.Selected = true;
}