[5.0] 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`
It should not be void also.

Currently, `Mailer::send()` return the results of `Swift_Mailer::send()` which is the number of recipients if I'm not mistaken.

`Mailer::raw()` returns the results of `Mailer::send()`, so the implementation is different from the contract.

Refer to: https://github.com/laravel/framework/commit/f86f59fc2e82a2ef8d66f745c0b8d15a41fb043a