DO NOT MERGE: Namespace support (Part 1)

Assuming #1114 is accepted, this PR is attempting to provide the first stage of namespace support.

1. Introduce Namespace concept on affected resource types
2. Modify RESTStorage interface to be namespace-aware
3. Default our HTTP handlers to hard-code to always work in the "default" namespace for now
4. Update etcd storage keys to use namespace
5. Keep unit tests functional

The idea is to keep our code-reviews in small enough chunks so they are understandable, and to get agreement on the initial pattern before taking on the additional work of:

1. Updating kubeclient to build namespace aware URIs
2. Updating kubecfg to set client specific ns

Right now, I treat ID as "Name" per the #1216 proposal, but I could rename it as part of this initial PR once things settle.