Handle deep nested relations. Forbid 2 fully identical stages.

[DavidKrpt]

1. Fixed the buildLookup function to carry forward not just the current and the parent relations, but all of the ancestor relation names. Now $unwind and $lookup paths should be built correctly for 3 level and deeper nested relations.
2. Before appending a stage perform a lodash deep equality to see if an identical stage already exists, if so, ignore the stage. Without this fix partially overlapping relation paths would result in multiple identical lookup and unwind stages for the overlapping parts of their paths, and each subsequent stage would overwrite the result of the previous one.

This PR doesn't address any of the remaining 2 issues, these are new.

[Akeri]

Very grateful for your contribution!
Published 1.1.3