Fix custom connection in database migrations

[antonkomarev]

Resolves #116

@vesper8 found that Migration's getConnection() method is used only for resolving if connection supports schema transactions, but never used in migration itself.

protected function runMigration($migration, $method)
{
    $connection = $this->resolveConnection(
        $migration->getConnection()
    );

    $callback = function () use ($migration, $method) {
        if (method_exists($migration, $method)) {
            $this->fireMigrationEvent(new MigrationStarted($migration, $method));

            $migration->{$method}();

            $this->fireMigrationEvent(new MigrationEnded($migration, $method));
        }
    };

    $this->getSchemaGrammar($connection)->supportsSchemaTransactions()
        && $migration->withinTransaction
                ? $connection->transaction($callback)
                : $callback();
}

So I've added protected $schema property with configured connection.

Additionally this PR fixes missing Schema configuration in love:setup-reacterable & love:setup-reactable commands.