Changed Tree Toolbar button icons and adjusted button spacing

src/main/java/edu/rpi/legup/ui/proofeditorui/treeview/TreePanel.java

@@ -28,7 +28,7 @@ public class TreePanel extends JPanel {
     private JPanel main;
     private TreeView treeView;
     private TreeToolbarPanel toolbar;
-    private LegupUI legupUI;
+    // private LegupUI legupUI;
 
     private JLabel status;
 

src/main/java/edu/rpi/legup/ui/proofeditorui/treeview/TreeToolBarButton.java

@@ -1,15 +1,18 @@
 package edu.rpi.legup.ui.proofeditorui.treeview;
 
 import javax.swing.*;
+import java.awt.Dimension;
 
 public class TreeToolBarButton extends JButton {
 
     private TreeToolBarName name;
+    private final Dimension MINIMUM_DIMENSION = new Dimension(60, 60);
 
     public TreeToolBarButton(ImageIcon imageIcon, TreeToolBarName name) {
         super(imageIcon);
         this.name = name;
-        this.setSize(60, 60);
+        this.setSize(MINIMUM_DIMENSION.width, MINIMUM_DIMENSION.height);
+        this.setMinimumSize(this.MINIMUM_DIMENSION);
     }
 
     public TreeToolBarName getToolBarName() {

src/main/java/edu/rpi/legup/ui/proofeditorui/treeview/TreeToolbarPanel.java

@@ -12,7 +12,8 @@ public class TreeToolbarPanel extends JPanel {
      */
     public TreeToolbarPanel(TreePanel treePanel) {
         this.treePanel = treePanel;
-        this.setLayout(new GridLayout(4, 1));
+        this.setLayout(new GridLayout(4, 1, 0, 2));
+
 
         addChild = new TreeToolBarButton(new ImageIcon(ClassLoader.getSystemResource("edu/rpi/legup/images/Legup/AddChild.png")), TreeToolBarName.ADD_CHILD);
         delChild = new TreeToolBarButton(new ImageIcon(ClassLoader.getSystemResource("edu/rpi/legup/images/Legup/DelChild.png")), TreeToolBarName.DEL_CHILD);