Added ability to set custom ldap group -> role mapping

Added input in role form to allow matching against custom names.
Changed default mapping to use role display name instead of the hidden
DB name.

database/migrations/2018_07_15_173514_add_role_external_auth_id.php

@@ -0,0 +1,33 @@
+<?php
+
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Migrations\Migration;
+
+class AddRoleExternalAuthId extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::table('roles', function (Blueprint $table) {
+            $table->string('external_auth_id', 200)->default('');
+            $table->index('external_auth_id');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        Schema::table('roles', function (Blueprint $table) {
+            $table->dropColumn('external_auth_id');
+        });
+    }
+}