Added account types model and migration.

database/migrations/2018_09_07_102147_create_account_types_table.php

@@ -0,0 +1,43 @@
+<?php
+
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Migrations\Migration;
+
+class CreateAccountTypesTable extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::create('account_types', function (Blueprint $table) {
+            $table->increments('id');
+            
+            // The name of the account type
+            $table->string('name');
+
+            // The account class to which the account type belongs
+            $table->integer('account_class_id')->unsigned();
+            $table->foreign('account_class_id')->references('id')->on('account_classes')
+                  ->onDelete('restrict');
+
+            // An unique number of the account type
+            $table->integer('number')->unique();
+            
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        Schema::dropIfExists('account_types');
+    }
+}