Hook up parse-env

This simplifies the configuration of the project somewhat and allows us
to use environment variables should we want to.
Set Jade version explicitly

Just to avoid some problems.
In case uptime is null, treat it as 1 instead

This way we won't get weird results on the frontend. Closes #34.
Set up Twitter share

Closes #29.
Allow cron expression to be defined via config

Closes #30.

Note that we still need to remember to set the expression right at the
server.