Improve usability by adding subheaders "Tour #1" to tours page
Disable submit button after submitting

Fixes #94
Fix specs
Throw 400 Bad Request if user provides invalid date
Merge pull request #95 from nubedianGmbH/95-api-invalid-date

Don't throw 500 if user provides invalid date
Fix current orders not being displayed on tours#index page
Don't squeeze a bazillion tours in one row
Let user remove tours from tour manager