Misc. cleanup

core/src/io/anuke/mindustry/ui/dialogs/TechTreeDialog.java

@@ -77,7 +77,7 @@ public class TechTreeDialog extends FloatingDialog{
         if(!locked) node.visible = true;
         for(TreeNode child : node.children){
             TechTreeNode l = (TechTreeNode)child;
-            l.visible = !locked;
+            l.visible = !locked && l.node.block.isVisible();
             checkNodes(l);
         }
     }

core/src/io/anuke/mindustry/ui/fragments/PlacementFragment.java

@@ -33,7 +33,7 @@ public class PlacementFragment extends Fragment{
     final int rowWidth = 4;
 
     Array<Block> returnArray = new Array<>();
-    Category currentCategory = Category.turret;
+    Category currentCategory = Category.distribution;
     Block hovered, lastDisplay;
     Tile hoverTile;
     Table blockTable, toggler, topTable;