Move some base classes into the API

Add Javadocs for API classes that didn't already have them

Redo

'nother redo

Another redo

Update ItemSigil.java

Last one, I swear

Fix

src/main/java/WayofTime/bloodmagic/api/iface/ISigil.java

@@ -1,5 +1,9 @@
 package WayofTime.bloodmagic.api.iface;
 
+/**
+ * Used for all {@link WayofTime.bloodmagic.api.impl.ItemSigil}
+ * <b>EXCEPT</b> Sigils of Holdings.
+ */
 public interface ISigil
 {
 }