OrderedSelect

In order to be able to reconstruct the original ordering of elements inside of a select clause, we need to keep track of their order, not only within the top-level select but also it's order within any possible tuples/case-classes that in which it is embedded. For example, in the query:

 query[Person].map(p => (p.id, (p.name, p.age))).nested
// SELECT p.id, p.name, p.age FROM (SELECT x.id, x.name, x.age FROM person
x) AS p 

Since the p.name and p.age elements are selected inside of a sub-tuple, their "order" is List(2,1) and List(2,2) respectively as opposed to p.id whose "order" is just List(1).

This class keeps track of the values needed in order to perform do this.