Fluent interface for Relation

[CodeLionX]

Issue

Add a new TransientRelation extends Relation for providing a fluent interface for dealing with Relations. Instantiation of TransientRelations should be only possible within the framework. It must not be visible outside of the framework as it only provides an implementation of all Relation's functions.

Problem Description

Most functions of Relation just return a Seq[Records]. So method chaining is not possible and we must fallback to functions on Seq:

val result: Seq[Records] = User
  .where(User.id => { _ == 22 })
  .map(_.project(Seq(User.id, User.name)).get)
  .sortBy(_.get(User.name))

Supporting Information

Desired syntax:

val result: Seq[Records] = User
  .where(User.id => { _ == 22 })
  .project(Seq(User.id, User.name))
  .orderBy(User.name)
  .records

[CodeLionX]

further changes in #45 and #46