Webtiles: get_titles.py: fix player_title_file param checking
Webtiles: rename server admins -> server owners

I'd like to add another group of users who can run some admin commands
but are not owners, this rename is to disambiguate the two groups.
Webtiles: add server janitors

Server Janitors are a new group, comprised of server owners, (possibly)
devs and other users as defined by the owners. They don't get special
group colouring in chat.

Janitors are given access to a new control panel exposed in webtiles,
which can be used for various administrative tasks, such as kicking off
a rebuild or download a save file.
Webtiles: config.toml.sample cosmetics
Webtiles: add janitor_commands

This implements a system for janitors to run pre-defined commands
through webtiles. The intended use case is for crawl-developers to
perform some behind-the-scenes administrative tasks, such as:
* Kicking off a manual trunk rebuild
* Downloading save games of users that help replicate bugs

The current implementation is experimental, with the following caveats:
* No action is actually taken, just debug logged
* There is no janitor user authentication on janitor commands(!!!)