GUI server: Deployer and DeployMiddleware.
This branch includes the bundles support
base classes. They are already described
in the bundles package docstring.
The diff is a bit long, sorry about that.
Most of the new code are tests.
The next branch will integrate and enable
the bundle support in the GUI server.
Tests: `make unittest` from the branch root.
R=benji, bac
CC=
https://codereview.appspot.com/12802045