Re-architect sea-orm depedency

[tyt2y3]

Okay so the culprit is that sea-orm and sea-schema each has a dependency on sea-query, currently stuck in a deadlock, and there is no way to upgrade one side without breaking the other side.

We definitely have to re-architect this before releasing. The problem is the API exposed sea-query symbols and that tied things together. Ideally, sea-schema should be able to use a different sea-query version internally from sea-orm without causing trouble.

The migrator should use the sea-query pubed by sea-orm, or ideally, not using the high level sea-query interface at all.

Originally posted by @tyt2y3 in #26 (comment)