Add mutable & immutable transaction interfaces and implementations, replacing copy()

Patchwork/src/main/java/me/totalfreedom/economy/CompletedTransaction.java

@@ -1,8 +1,7 @@
 package me.totalfreedom.economy;
 
-public interface CompletedTransaction
+public interface CompletedTransaction extends Transaction
 {
-    Transaction getTransaction();
 
     TransactionResult getResult();
 }

Patchwork/src/main/java/me/totalfreedom/economy/MutableTransaction.java

@@ -0,0 +1,13 @@
+package me.totalfreedom.economy;
+
+/**
+ * Please ensure that all modifications of {@link MutableTransaction} happen BEFORE it is passed to a {@link Transactor} implementation
+ */
+public interface MutableTransaction extends Transaction
+{
+    long addToBalance(final long amount);
+
+    long removeFromBalance(final long amount);
+
+    void setBalance(final long newBalance);
+}

Patchwork/src/main/java/me/totalfreedom/economy/Transaction.java

@@ -2,17 +2,10 @@ package me.totalfreedom.economy;
 
 public interface Transaction
 {
-    Transaction copy();
-
     EconomicEntity getSource();
 
     EconomicEntity getDestination();
 
     long getBalance();
 
-    long addToBalance(final long amount);
-
-    long removeFromBalance(final long amount);
-
-    void setBalance(final long newBalance);
 }

Patchwork/src/main/java/me/totalfreedom/economy/Transactor.java

@@ -2,5 +2,5 @@ package me.totalfreedom.economy;
 
 public interface Transactor
 {
-    CompletedTransaction handleTransaction(Transaction transaction);
+    CompletedTransaction handleTransaction(MutableTransaction transaction);
 }