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...)
Simplify webtiles config file loading error handling

Conflicts:
	crawl-ref/source/webserver/conf.py
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.
Add [[games]] options example to first game in config.toml.sample
Add webserver conf.games.d/
rework some webtiles games_conf_d logging
Make config.dgl_status_file optional
Check config.dgl_status_file writability on startup

Strictly speaking the server runs fine even if you can't write this
file, but since it's an optional setting we assume that setting this
option means the user cares about it.
Add some debug logging around webtiles listen socket setup
Add enable_access_log webtiles option
Add a bit more config.toml.sample documentation
WebTiles cross-site protection should ignore protocol mismatch
fix whitespace
Remove unneccessary try/except block
fix conf path loading issues
Add webtiles startup check for config.password_db
Make init_player_program optional, but error if it's set badly
Make 'init_player_program failure' message more generic