Make rebuildable a block attribute (#1338)

core/src/mindustry/world/Block.java

@@ -55,6 +55,8 @@ public class Block extends BlockStorage{
     public boolean rotate;
     /** whether you can break this with rightclick */
     public boolean breakable;
+    /** whether to add this block to brokenblocks */
+    public boolean rebuildable = true;
     /** whether this floor can be placed on. */
     public boolean placeableOn = true;
     /** whether this block has insulating properties. */

core/src/mindustry/world/blocks/defense/ShockMine.java

@@ -26,6 +26,7 @@ public class ShockMine extends Block{
         solid = false;
         targetable = false;
         layer = Layer.overlay;
+        rebuildable = false;
     }
 
     @Override

core/src/mindustry/world/blocks/power/NuclearReactor.java

@@ -46,6 +46,7 @@ public class NuclearReactor extends PowerGenerator{
         hasItems = true;
         hasLiquids = true;
         entityType = NuclearReactorEntity::new;
+        rebuildable = false;
     }
 
     @Override