Allow dying pocket computers too

This splits up the pocket computer textures and models into the frame
(off, on, blinking), colour layer (normal, advanced, custom) and modem
light.

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

@@ -22,6 +22,24 @@ public interface IPocketAccess
     @Nullable
     Entity getEntity();
 
+    /**
+     * Get the colour of this pocket computer as a RGB number.
+     *
+     * @return The colour this pocket computer is. This will be a RGB colour between {@code 0x000000} and
+     * {@code 0xFFFFFF} or -1 if it has no colour.
+     * @see #setColour(int)
+     */
+    int getColour();
+
+    /**
+     * Set the colour of the pocket computer to a RGB number.
+     *
+     * @param colour The colour this pocket computer should be changed to. This should be a RGB colour between
+     *               {@code 0x000000} and {@code 0xFFFFFF} or -1 to reset to the default colour.
+     * @see #getColour()
+     */
+    void setColour( int colour );
+
     /**
      * Get the colour of this pocket computer's light as a RGB number.
      *