mailing on creation and ability for viewing ticket details without being logged in added

# What is this?

This PR introduces notifications into the app so that everytime a ticket it created the user is notified with a url to the ticket details.

Also, the ticket details action can now be accessed without any user being logged in.

# Anything else?

Yep, added `:letter_opener` for email previews AND some mailer helpers for rspec.