Make hackathon contact email customizable

[SaltyQuetzals]

Is your feature request related to a problem? Please describe.
A lot of mailto: links are hard-coded to be TAMUhack-specific right now. It'd be nice if we added another customization setting like CONTACT_EMAIL_ADDRESS so that organizers can just set-and-forget the emails. If multiple emails are needed, settings for those could be created as well for more granularity.

Describe the solution you'd like
A new setting in hiss/hiss/settings/customization.py that allows organizers to quickly swap out email addresses to fit their custom event.

References to a hard-coded email would need to be replaced and tested so that they include this variable in their template context.