Server logs with timestamp archived in daily files

Adds basic structured logging to the luigi server with spooled daily output files.
It was previously lacking timestamps and "logged" by capturing stdout/stderr to a single ever-growing log file.

There is still a lot room for improvement for logging like adding configuration (#137) and improving the client-side logging (they can probably share a lot of code) but in the context of continuous improvement, this patch is definitely one and it will help a lot when tracking down bugs or weird behaviour in the scheduler.