Several minor improvements

- Restrict what items can be inserted into printers. They're now closer
   to brewing stands or furnaces: nothing can go in the output slot,
   only ink in the ink slot, and only paper in the paper slot.
 - Fix build.gradle using the wrong version
 - Trim the width of tables to fit when displaying on the client. Closes
   #45. Note, our solution isn't perfect, as it will wordwrap too, but
   it's adaquate for now.

src/main/java/dan200/computercraft/shared/util/ValidatingSlot.java

@@ -0,0 +1,25 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2019. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.shared.util;
+
+import net.minecraft.inventory.IInventory;
+import net.minecraft.inventory.Slot;
+import net.minecraft.item.ItemStack;
+
+public class ValidatingSlot extends Slot
+{
+    public ValidatingSlot( IInventory inventoryIn, int index, int xPosition, int yPosition )
+    {
+        super( inventoryIn, index, xPosition, yPosition );
+    }
+
+    @Override
+    public boolean isItemValid( ItemStack stack )
+    {
+        return true; // inventory.isItemValidForSlot( slotNumber, stack );
+    }
+}