Add compound query support for AioModel

[kalombos]

This code should work:

query = (
    TestModel.select().where(TestModel.id == obj1.id) |
    TestModel.select().where(TestModel.id == obj2.id)
)
await query.aio_execute()

[spumer]

This is really correct query for Peeweee? D:

[kalombos]

Yeah. Here is an example. The issue is about backward compatibility mostly since the query works if you use manager. The problem is there are a lot of cases for contstructing such queries. Here is and here is and here is. I think fixing the query is enough for first iteration :)