Moving keeps everything in the /matrix directory, so that we
wouldn't contaminate anything else on the system or risk
clashing with something else.

Also retrieving certificates separately for the Riot and Matrix domains,
which should help in multiple ways:

- allows them to be very different (completely separate base domain..)

- allows for Riot to be disabled for the playbook some time later
  and still have the code not break

The goal is to allow these to be on separate partitions
(including remote ones in the future).

Because the `silviof/docker-matrix` image chowns
everything to MATRIX_UID:MATRIX_GID on startup,
we definitely don't want to include `media_store` in it.
If it's on a remote FS, it would cause a slow startup.

Also, adding some safety checks to the "import media store"
task, after passing a wrong path to it on multiple occassions and
wondering what's wrong.

Also, making logging configurable. The default of keeping 10x100MB
log files is likely excessive and people may want to change that.

By using role defauts, we can have inventory variables
which overide the defaults.