Merge tag '0.9' into develop

0.9 (2018-04-17)
----------------

Features:

- Add internationalization support (#5)
- Can now follow and import music from remote libraries (#136, #137)

Enhancements:

- Added a i18n-extract yarn script to extract strings to PO files (#162)
- User admin now includes signup and last login dates (#148)
- We now use a proper user agent including instance version and url during
  outgoing requests

Federation is here!
^^^^^^^^^^^^^^^^^^^

This is for real this time, and includes:

- Following other Funkwhale libraries
- Importing tracks from remote libraries (tracks are hotlinked, and only cached for a short amount of time)
- Searching accross federated catalogs

Note that by default, federation is opt-in, on a per-instance basis:
instances will request access to your catalog, and you can accept or refuse
those requests. You can also revoke the access at any time.

Documentation was updated with relevant instructions to use and benefit
from this new feature: https://docs.funkwhale.audio/federation.html

Preparing internationalization
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Funkwhale's front-end as always been english-only, and this is a barrier
to new users. The work make Funkwhale's interface translatable was started
in this release by Baptiste. Although nothing is translated yet,
this release includes behind the stage changes that will make it possible in
the near future.

Many thank to Baptiste for the hard work and for figuring out a proper solution
to this difficult problem.

Upgrade path
^^^^^^^^^^^^

In addition to the usual instructions from
https://docs.funkwhale.audio/upgrading.html, non-docker users will have
to setup an additional systemd unit file for recurrent tasks.

This was forgotten in the deployment documentation, but recurrent tasks,
managed by the celery beat process, will be needed more and more in subsequent
releases. Right now, we'll be using to clear the cache for federated music files
and keep disk usage to a minimum.

In the future, they will also be needed to refetch music metadata or federated
information periodically.

Celery beat can be enabled easily::

    curl -L -o "/etc/systemd/system/funkwhale-beat.service" "https://code.eliotberriot.com/funkwhale/funkwhale/raw/develop/deploy/funkwhale-beat.service"
    # Also edit /etc/systemd/system/funkwhale.target
    # and ensure the Wants= line contains the following:
    # Wants=funkwhale-server.service funkwhale-worker.service funkwhale-beat.service
    nano /etc/systemd/system/funkwhale.target
    # reload configuration
    systemctl daemon-reload

Docker users already have celerybeat enabled.