resolve route by `branchAndPath` for blobs as well

Tree routes are specified by the `branchAndPath` params, so the Blob
routes should be as well for consistency sake. A side effect of this is
that the model hook for blobs and trees are guaranteed to be call when
clicking from a link-to helper because the link-to helper's context are
now just strings instead of objects. We can remove setupController calls
which were there to load "detailed" properties of the models after
transitions.
cache tree results after API call

Improve's performance a little bit, although I think rendering a tree is
taking the most time especially when the tree has many many files.