[WIP/Need Help] Redirect stdio to a file with synctl --daemonize

[SohamG]

Attempt to fix #1539

Changes

• Added synapse/app/_daemonize.py inspired by daemonize but stripped down.
• Used the file above to redirect stdio/stderr to a file (default "homserver.out")
• Added config option for "homeserver.out"
• Ignored --no-redirect-stdio

Need Help!

• Still need to properly separate the two files by changing twisted's log config. This looks like a pretty huge task, especially cause I'm not familiar with twisted (I'm in the process of learning twisted)
• Need to find a better/more elegant way of warning --no-redirect-stdio is ignored, ie the warning should be printed only if the option is used etc
• Need to finish the license header for _daemonize.py. The file is very similar to the original, I don't know how to copyright/license it.
• Need to know what else is needed to be done to finish this

Disclaimer

I'm pretty unfamiliar with the codebase and twisted. Hence, there's a good chance this PR is a bugfest. I'd love to learn and make changes though 😃

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file
• Pull request includes a sign off

[richvdh]

@SohamG: I've only had a chance to skim the changes, so I may be way off-base here, but my main advice to you would be: change fewer things at once. Smaller PRs are much easier for us to review and for you to get bug-free. So for instance: start with a PR which just replaces daemonize with our own version.

[SohamG]

@richvdh Thanks that really seems like a good idea. I'll get to work!