Adds support for managing certificates manually and for
having the playbook generate self-signed certificates for you.

With this, Let's Encrypt usage is no longer required.

Fixes Github issue #50.

Pretty much all variables live in their own `matrix_<whatever>`
prefix now and are grouped closer together in the default
variables file (`roles/matrix-server/defaults/main.yml`).

`--log-driver=none` is used for all Docker containers now.

All these containers are started through systemd anyway and get logged in journald,
so there's no need for Docker to be logging the same thing using the default `json-file` driver.
Doing that was growing `/var/lib/docker/containers/..` infinitely until service/container restart.

As a result of this, things like `docker logs matrix-synapse` won't work anymore.
`journalctl -u matrix-synapse` is how one can see the logs.

I've found the previous 10K default value to be way too low
on a bunch of servers I'm running, so it's now up to
100K and made configurable.

Closes Github issue #5

Closes Github issue #3

Regression since a302a7d7489ec,
which made the Matrix Client API only available on
the http port (8008) and not over the federation port (8448).

This disables federation on the 80 port, as it's
not necessary. We also disable the old Angular webclient.

For the federation port (8448), we disable the client APIs
as those are not necessary. Those can even cause trouble
if one doesn't know about them and thinks that guarding the client
APIs at the 80 port is enough.

Moving away from using the default bridge network to using our own.
This isolates our services from other Docker containers running
on the default network on the same host.

The benefits are that:

- isolation is a little better - we no longer share a default
bridge network with any other containers that might be running on the host

- there are no longer hard dependencies - we do service discovery
by DNS name, and not via explicit `--link` usage during container start,
so containers can start out of order and fail without bringing down others
with them
(`matrix-nginx-proxy` can continue running, even if one of the other services dies)

In the future, when other services get introduced,
the increased resilience and simplicity will help as well.