Only includes relations eagerly included

[zoriya]

On #90 and #92, I added navigation queries on the last .Select call to keep included properties on the returned entities, but doing so actually made EF fetch all relations of this item. This PR actually reads .Include calls to prevent unnecessary fetching.

With an example:

db.Set<User>()
    .Include(x => x.Orders)
    .First();

resulted in

db.Set<User>()
    .Include(x => x.Orders)
    .Select(x => new User{
        Id = x.Id,
        Name = x.Name,
        Orders = x.Orders,
        Friends = x.Friends // Here relation friends is fetched but it was not requested. This can create really slow queries.
    })
    .First();

and after this PR this generates:

db.Set<User>()
    .Include(x => x.Orders)
    .Select(x => new User{
        Id = x.Id,
        Name = x.Name,
        Orders = x.Orders,
        // No Friends requeseted here.
    })
    .First();

Filtered includes (like in the example below) are not parsed, and I don't know how they should be handled.

db.Set<User>()
    .Incude(x => x.Orders.Where(x => x.Price > 100));

I also made root query rewriting use properties directly instead of their baking fields (it was way simpler than I thought).

Based on #91 since include parsing was needed and was already done.

[zoriya]

Also, something I just found out, but query can't be tracked when root rewriting is enabled. Something we might want to consider to decide if OnlyOnInclude should default to true or false.