Extracted contracts

Extracted Database, View, Validation, Translation and Queue contracts.

Fixed some typos along the way

Only ones remaining are:
* `Illuminate\Routing\Annotations\EndpointInterface`
* `Illuminate\Routing\Matching\ValidatorInterface`
And everywhere else. `@return` annotations MUST immediately follow `@param` annotations.

See what I mean about us wasting time correcting docblock formatting @taylorotwell.