Namespace package declaration to make setuptools happy
Explicit version requirements on a formulas

Right now the only check supported is ==. Given I'm mandating SemVer we could possible just convert everything to ~> style comparison.
Fix bug where formula requirement as a branch wouldn't get updated.
Allow (and enable by default) versions of to be overridden from top level formula-requirements.txt

This is a "short term" (ha!) work around to avoid dependancy hell.
Extract out the formula manager into a separate class called Shaker.

Sym did most of this work already in is UCC-deploy repo, I've (Ash) just
copied the strucutre and functions for the updated version here.
Fix the broken "refactor" to correctly symlink the directories
And fix nested requirements after the restructure
fix conflict resolution
resolve correctly sha revision
remove debug & pythonic mkdir
Merge pull request #11 from ministryofjustice/versioned-formula-reqs

Versioned formula reqs manager - tested