Move STDOUT logger creation App => bin/ryespy and remove App#logger .

Note that the log level cannot be set in `App#initialize`, since that
would call `#config` before it's been configured by `#configure`,
meaning the DEBUG 'Configured' wouldn't appear.

Also note that this approach prevents `Config#log_level` from being
set without going through `#configure`, but this is probably alright.
Remove App#config , changing to getter only.

It's probably a little nicer if `@config` setter is not exposed
directly, also considering that it does not set the log level properly.
Besides, there's no need.