cronjob general alarms

[jessebot]

tidy up the existing alarms in cron/ and make them configurable via the onboardme script.

For script, default install lunch, bedtime, and break alarms.

--cron-alarms should default to default, but should take ['work','none']

--muted-alarms should default to false, but should action=store_true

Add a part of the cronjob script that checks for ~/.do-not-disturb file, and will automatically set alarms to silent.

[jessebot]

I don't like my original suggestion anymore now that I know about the XDG Base Directory Spec. I will instead be putting these in $XDG_CONFIG_HOME/onboardme/cron (with XDG_CONFIG_HOME defaulting to ~/.config if it's not set).