Preparations to include powerline-daemon into main powerline tree

Changes:

- Code style fixes.
- Made it respect `--config` and `--theme_option` arguments.
- Made it use one `config_loader` object for all `Powerline` instanses.
- Support for `args.renderer_arg` (required for tmux + cwd).
- Removed file that is no longer used.

Requires Lokaltog/powerline#476 to be merged.