Clean up migrations

* Make filenames and order more consistent

* Split foreign keys into their own migrations, add statements to ensure
  data integrity prior to adding them

* Add renameColumns helper, use other helpers where possible

migrations/2018_01_18_133000_change_notifications_columns.php

@@ -0,0 +1,64 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Schema\Builder;
+
+return [
+    'up' => function (Builder $schema) {
+        $schema->table('notifications', function (Blueprint $table) {
+            $table->dropColumn('sender_id', 'subject_type');
+
+            $table->renameColumn('time', 'created_at');
+
+            $table->timestamp('read_at')->nullable();
+            $table->timestamp('deleted_at')->nullable();
+        });
+
+        $schema->getConnection()->table('notifications')
+            ->where('is_read', 1)
+            ->update(['read_at' => time()]);
+
+        $schema->getConnection()->table('notifications')
+            ->where('is_deleted', 1)
+            ->update(['deleted_at' => time()]);
+
+        $schema->table('notifications', function (Blueprint $table) {
+            $table->dropColumn('is_read');
+            $table->dropColumn('is_deleted');
+        });
+    },
+
+    'down' => function (Builder $schema) {
+        $schema->table('notifications', function (Blueprint $table) {
+            $table->integer('sender_id')->unsigned()->nullable();
+            $table->string('subject_type', 200)->nullable();
+
+            $table->renameColumn('created_at', 'time');
+
+            $table->boolean('is_read');
+            $table->boolean('is_deleted');
+        });
+
+        $schema->getConnection()->table('notifications')
+            ->whereNotNull('read_at')
+            ->update(['is_read' => 1]);
+
+        $schema->getConnection()->table('notifications')
+            ->whereNotNull('deleted_at')
+            ->update(['is_deleted' => 1]);
+
+        $schema->table('notifications', function (Blueprint $table) {
+            $table->dropColumn('read_at');
+            $table->dropColumn('deleted_at');
+        });
+    }
+];