Some further cleanup and 1.13 cherry-picks

Are most of these changes small and petty? Yes. However, IMO they do
make the code more readable. Anyway, a summary of some of the more
interesting changes:

 - Expose Abstract*Upgrade classes in the API
 - Fix the spelling of Jonathan in the API docs (*shakes fist*)
 - Fix bug with printout not working in the offhand.
 - Rename any argments/variables accidentally named "m_*", and add an
   inspection to prevent it happening again.
 - Remove most of the Block*.Properties classes - just inline them in
   the parent class.
 - Return super.writeToNBT instead of reassigning at the top.

src/main/java/dan200/computercraft/api/pocket/AbstractPocketUpgrade.java

@@ -0,0 +1,57 @@
+/*
+ * 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.api.pocket;
+
+import net.minecraft.item.ItemStack;
+import net.minecraft.util.ResourceLocation;
+
+import javax.annotation.Nonnull;
+
+/**
+ * A base class for {@link IPocketUpgrade}s.
+ *
+ * One does not have to use this, but it does provide a convenient template.
+ */
+public abstract class AbstractPocketUpgrade implements IPocketUpgrade
+{
+    private final ResourceLocation id;
+    private final String adjective;
+    private final ItemStack stack;
+
+    protected AbstractPocketUpgrade( ResourceLocation id, String adjective, ItemStack stack )
+    {
+        this.id = id;
+        this.adjective = adjective;
+        this.stack = stack;
+    }
+
+    protected AbstractPocketUpgrade( ResourceLocation id, ItemStack stack )
+    {
+        this( id, "upgrade." + id + ".adjective", stack );
+    }
+
+    @Nonnull
+    @Override
+    public final ResourceLocation getUpgradeID()
+    {
+        return id;
+    }
+
+    @Nonnull
+    @Override
+    public final String getUnlocalisedAdjective()
+    {
+        return adjective;
+    }
+
+    @Nonnull
+    @Override
+    public final ItemStack getCraftingItem()
+    {
+        return stack;
+    }
+}