Add failing test for invalid url

Events are currently allowed to be saved with invalid urls, resulting in broken
links on the event view page. In particular, urls with spaces in them are not
triggering the url validator in the Event model.

I added failing tests for invalid urls and passing tests for valid urls
Refactor url validator in Event model

The regex used by the url validator was allowing invalid urls to be saved.
Urls of the form `example.com, http://www.example.com` were allowed to be
persisted to the database. Added a ^ to the regex to start it at the beginning
of the line, and simplified how it checked for the http/https scheme.
Refactor url validator test to use `let`

The url validator test defined each set of test urls wth a heredoc statement
and then split it with String#gsub and String#split. That was silly.

Refactored to use Rspec `let` method.
Update validator to reject urls with a newline.

Adds a test case for a url with a newline character, updates the validator
regexp to match the entire string. Also removes some debugging code left in by
accident.
Replace be_falsey with be_valid
Merge pull request #128 from jmromer/fix_url_validator

Fix url validator