* ui: Add Admin Partition feature flag
This adds a `PartitionEnabled`/`CONSUL_PARTITIONS_ENABLED` feature flag
that can be set during production form the consul binary, or
additionally during development/testing via cookies.
* Add partitions bookmarklet and docs, and all eng docs from main README to the docs instead.
You probably already have the app running once you need these, and it reduces the amount of text/detail in the main README
* Add the env variable section back into the README with actual env vars
