Named tree transformations

[ggevay]

We would like Common.pipeline to know the names of the transformations, so that it can log times (and possibly other useful stuff).

For this, instead of
transformations: (u.Tree => u.Tree)*
it should take
transformations: TreeTransform*
where TreeTransform is a case class with a u.Tree => u.Tree and a name string.

TreeTransform should have an implicit conversion from u.Tree => u.Tree, (with an empty name), to avoid having to name every transformation in the whole codebase right away.

[ggevay]

Done with #360