Regression since #362 (Github Pull Request).

This reverts commit 61e93744ec.

Reverting because of:
- https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/341
- https://github.com/matrix-org/matrix-appservice-slack/issues/347

Synapse v1.9.0 changed some things which made the REST Auth Password
Provider break.

The ma1uta/matrix-synapse-rest-password-provider implements some
workarounds for now and will likely deliver a proper fix in the future.

Not much has changed between the 2 projects, so this should be a
painless transition.

This change allows us to work with both our existing Docker image
(`tedomum/matrix-appservice-irc:latest`) and with the
official Docker image (`matrixdotorg/matrix-appservice-irc`).

The actual change to the official Docker image requires more testing
and will be done separately.

Related to #355.

Regression introduced in 53186ffa1c

NeDB is deprecated, so we should transition away from it in the future.
Still, most of the functionality should work on this new version.

Related to #330 (Github Issue).

Fixes #330 (Github Issue).

This allows for users to bridge already existing matrix rooms to discord

https://github.com/matrix-org/matrix-doc/pull/1957

Yay Riot iOS now supports integration manager discovery!