Cherry pick several improvements from 1.13

- Move container opening (and gui handling) into a separate class
 - Move turtle/computer placement code onto the block
 - GUIs now use gui{Left,Top} instead of calculating it manually.
 - IPeripheralTile is now exposed in the API.

src/main/java/dan200/computercraft/api/peripheral/IPeripheralProvider.java

@@ -6,6 +6,7 @@
 
 package dan200.computercraft.api.peripheral;
 
+import net.minecraft.tileentity.TileEntity;
 import net.minecraft.util.EnumFacing;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.World;
@@ -16,6 +17,8 @@ import javax.annotation.Nullable;
 /**
  * This interface is used to create peripheral implementations for blocks.
  *
+ * If you have a {@link TileEntity} which acts as a peripheral, you may alternatively implement {@link IPeripheralTile}.
+ *
  * @see dan200.computercraft.api.ComputerCraftAPI#registerPeripheralProvider(IPeripheralProvider)
  */
 @FunctionalInterface