Merge branch 'develop'

Fixed dynamic upload type name (rebing#126)

Default params_key from params to variables

Support additional route group attributes (rebing#123)

fix custom controller for graphiql (rebing#121)

fix custom controller for graphiql

Added ability to customise validation errors (rebing#113)

* Added ability to customise validation errors

* Added documentation for validation
Made validationErrorMessages a method that can be overridden

* Update Readme.md

* Update Field.php

Added support for security rules

Add support for Unions (rebing#91)

* Add support for UnionType, refs rebing#63

* Extract Union functionality into extra class UnionType

* Add documentation for Union Types

Update Query.php (rebing#90)

* Update Query.php

Validation Rules should also apply to queries, just like it is for mutations.
The server should be able to catch validation errors and return proper messages whether the request is a query or a mutation.

* Update Field.php

* Update Query.php

* Update Mutation.php

Alias field (rebing#86)