provision/docker: store the version of the container on deploy

This will be necessary to use the proper version on AddUnits.

Related to #458.
exec/testing: fix dead lock caused by wrong method call
provision/docker: use the saved version to deploy new units

Related to #458.
api: read version from the body in cloneRepositoryHandler

This is a incompatible change :)

Related to #458.
api: change the HTTP method for cloneRepository

That is what I call "breaking compatibility" :)

Related to #458.
misc/git-hooks: running deploy on pre-receive

Closes #458.
misc/git-hooks: remove post-receive