Moved utf8mb4 migration to command instead of migration

To prevent errors upon migration.
Command generates out the SQL syntax to make the change instead
so the upgrade can be done manually.

In reference to #425

app/Console/Commands/UpgradeDatabaseEncoding.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace BookStack\Console\Commands;
+
+use Illuminate\Console\Command;
+use Illuminate\Support\Facades\DB;
+
+class UpgradeDatabaseEncoding extends Command
+{
+    /**
+     * The name and signature of the console command.
+     *
+     * @var string
+     */
+    protected $signature = 'bookstack:db-utf8mb4-syntax {--database= : The database connection to use.}';
+
+    /**
+     * The console command description.
+     *
+     * @var string
+     */
+    protected $description = 'Generate SQL commands to upgrade the database to UTF8mb4';
+
+    /**
+     * Create a new command instance.
+     *
+     */
+    public function __construct()
+    {
+        parent::__construct();
+    }
+
+    /**
+     * Execute the console command.
+     *
+     * @return mixed
+     */
+    public function handle()
+    {
+        $connection = DB::getDefaultConnection();
+        if ($this->option('database') !== null) {
+            DB::setDefaultConnection($this->option('database'));
+        }
+
+        $database = DB::getDatabaseName();
+        $tables = DB::select('SHOW TABLES');
+        $this->line('ALTER DATABASE `'.$database.'` CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;');
+        $this->line('USE `'.$database.'`;');
+        $key = 'Tables_in_' . $database;
+        foreach ($tables as $table) {
+            $tableName = $table->$key;
+            $this->line('ALTER TABLE `'.$tableName.'` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;');
+        }
+
+        DB::setDefaultConnection($connection);
+    }
+}