Added IO_type migration.

Changed person_targets migration to use a foreign key to the io_types table
instead of an enum.

database/migrations/2018_09_03_091643_create_person_targets_table.php

@@ -31,7 +31,9 @@ class CreatePersonTargetsTable extends Migration
             // The type of the target. It can be either a payable or a
             // receivable. A payable is of type 'expediture' and a receivable is
             // of type 'income'.
-            $table->tinyInteger('io_type');
+            $table->integer('io_type')->unsigned();
+            $table->foreign('io_type')->references('id')->on('io_types')
+                  ->onDelete('no action');
 
             // A reference text which describes the target
             $table->string('reference');

database/migrations/2018_09_07_075622_create_io_types_table.php

@@ -0,0 +1,34 @@
+<?php
+
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Migrations\Migration;
+
+class CreateIOTypesTable extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::create('io_types', function (Blueprint $table) {
+            $table->increments('id');
+            
+            $table->string('type')
+
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        Schema::dropIfExists('io_types');
+    }
+}