PHP Doublets Adapter via GraphQL client

[Konard]

This adapter should provide standard Doublets CRUD operations API in the native to PHP code style (the most commonly used one).
The libraries' architecture should take in account the ability to swap GraphQL with a native library that will be shipped later (when we finish translation to C++).
The GraphQL client layer should be usable separately as well as native to PHP's API.
It should be made as package for Pear2/Composer.