Refactor Webtiles config loader to accept an external config path

Not used yet, but will let us specify config path as a commandline
parameter rather than env var.
PEP8-ise a few files.

Following (mostly) guidelines from PEP8 as per flake8 utility.
chmod +x get_titles.py
webserver check_config outputs errors, not warnings
Experimental webtiles support for games.conf.d/

Add support for games_conf_d option, which sets a dir where additional
*.toml files specifying game configuration will be loaded from. Issues
with this initial support:

* Debug logging is hackily implemented through another env var (long
  term solution: allow passing logging parameters to server.py argv)
* Poor error handling for unexpected content in the additional toml
  files.
* Code to load additional config is very complex (hopefully mostly due
  to extensive error handling...)
Webtiles: Small documentation improvements.
Merge branch 'webtiles-changes' of https://gitorious.org/crawl/crawl into webtiles-changes

Conflicts:
	crawl-ref/source/webserver/conf.py
Simplify webtiles config file loading error handling
chown webserver pidfile as per config, so you can remove it on shutdown
Silence error during webserver shutdown

This happened to me on OSX with no games specified, I'm not sure what
the root cause is but seems harmless.