This reverts commit 3420a145, reversing
changes made to afb66a5a.

Inserted spaces in the name of Rails components.

Since I was on it, also used PostgreSQL instead of Postgres
because albeit Postgres is an accepted alias, PostgreSQL is
the official name and the actual name of the adapter.

See

    https://wiki.postgresql.org/wiki/ProjectName

with regard to PostgreSQL vs Postgres.

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

They're all at risk of races on the first requests.

- adapter -> pubsub (re)rename internally
- Change variable names to match method names
- Add EventMachine `~> 1.0` as a runtime dependency of ActionCable
- Refactor dependency loading for adapters

- Escape the channel name when subscribing in PG
- Refactor popping the queue to make it easier to read

We now only create one adapter instance for the server, so it can hold
the listener. This in turn allows the listener to get the PG connection
from the adapter, which will be a good place to allow more flexible
configuration.