Added support for stdClass collections

[obrunsmann]

Problem:

When creating export from a custom statement like

\DB::table('users')→select('email', 'name')→get()

Each row is an instance of \stdClass and we cannot access toArray(). This PR catches the case of a \stdClass row and converts it to an array.

[obrunsmann]

@rap2hpoutre can this be merged?