Access to HTTP Request in resolvers

This release comes with one new main feature: A custom GraphQLContext that is available in all resolvers and allows access to the current HTTP request:

<?php
// ...
use Wwwision\GraphQL\GraphQLContext;
// ...

  'resolve' => function ($value, array $args, GraphQLContext $context) {
    $baseUri = $context->getHttpRequest()->getBaseUri();
    // ...
  },

Apart from that this update incorporates some smaller improvements:

• FEATURE: Upgrade GraphiQL JS lib to v0.10.2
• FEATURE: Upgrade webonyx/graphql-php to 0.9.8
• TASK: Add unit test for HttpOptionsComponent
• TASK: Explicitly set the query action format to JSON
• TASK: Cosmetic fix to default Settings
• TASK: Mention Options HTTP Component in README