improve docker-compose

[gnouts]

Fix : #715

[eddyparkinson]

Thanks for the fix.

Has this been tested. Maybe a new install to check everything still installs?
Redis is optional, it should run with or without redis.
Please post some details of testing done. Thanks.

[gnouts]

Yes I've tested it on my local computer.

Indeed it could be good to choose to use Redis or not. I didn't want to go to this complexity. I just wanted to fix some unwanted behaviour that could break server, not improving things. ^^
But while I talk about it, I don't think mounting redis db as a volume is needed at all. But maybe it used to be needed for something ?

You can test it easily by running docker-compose up from the repo directory (supposing you have docker+docker-compose)