registration 7.x-1.0-alpha4

Changes since 7.x-1.0-alpha3:

• Fixing a couple typos.
• Removing unused registration_get_properties() function.
• Add missing Registration properties.
• Change registration_view function to use Registration::view().
• Move URI callback into entity class.
• Change registration class name from RegistrationEntity to just Registration.
• Fix slots validation in registration form.
• #1462138: Fix typo in confirmation message.
• #1316236: Add open and close dates for registrations.
• #1473460 by lsolesen: Missing space in constructor.
• Add registration_entity_access() callback and a "delete own registration" permission. Ref #1468520.
• #1467756: Remove mention of tours.
• Update return value in registration_save() and set default values in entity class. Ref #1418080.