New DeepSea PHP SDK 

PHP SDK has been restructured.

- Namespace `DeepSea\SDK` has been deprecated, replaced with `DeepSea\DeepSea`
- AccessToken is now partially managed by a session handled by `DeepSea\DeepSea`
- Added `Mockery` for `required-dev`

@felixkurniawan, @hermesvgani, and @rezanachmad Please help review and check