Encode URLs before saving them to the database

Otherwise the notifications will fail with
URI::InvalidURIError: bad URI(is not URI?)

```

irb(main):009:0> CASino::ServiceTicket.where('service like "%test%"').first.service
 CASino::ServiceTicket Load (0.2ms)  SELECT `casino_service_tickets`.* FROM `casino_service_tickets` WHERE (service like "%test%") LIMIT 1
=> "https://example.org/This is a test/dscn0115.jpg"

irb(main):013:0> CASino::ServiceTicket.where('service like "%test%"').first.send(:send_single_sign_out_notification)
 CASino::ServiceTicket Load (0.4ms)  SELECT `casino_service_tickets`.* FROM `casino_service_tickets` WHERE (service like "%test%") LIMIT 1
URI::InvalidURIError: bad URI(is not URI?): https://example.org/This is a
test/dscn0115.jpg
       from /usr/lib/ruby/1.9.1/uri/generic.rb:1202:in `rescue in merge'
       from /usr/lib/ruby/1.9.1/uri/generic.rb:1199:in `merge'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/faraday-0.8.8/lib/faraday/connection.rb:303:in `build_exclusive_url'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/faraday-0.8.8/lib/faraday/request.rb:94:in `to_env'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/faraday-0.8.8/lib/faraday/connection.rb:252:in `run_request'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/faraday-0.8.8/lib/faraday/connection.rb:118:in `post'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/faraday-0.8.8/lib/faraday.rb:24:in `method_missing'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/casino-2.0.2/app/models/casino/service_ticket/single_sign_out_notifier.rb:30:in `send_notification'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/casino-2.0.2/app/models/casino/service_ticket/single_sign_out_notifier.rb:10:in `notify'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/casino-2.0.2/app/models/casino/service_ticket.rb:40:in `send_single_sign_out_notification'
       from (irb):13
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/railties-3.2.17/lib/rails/commands/console.rb:47:in `start'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/railties-3.2.17/lib/rails/commands/console.rb:8:in `start'
       from /home/www-data/sso/shared/bundle/ruby/1.9.1/gems/railties-3.2.17/lib/rails/commands.rb:41:in `<top (required)>'
       from script/rails:6:in `require'
       from script/rails:6:in `<main>'
```