Add support for handling friends requests

[empyrical]

This pull request does the following:

• Adds a new sendUnrealClientDeleteRequest static method to FortniteClient.php for sending DELETE requests to Unreal Client endpoints
• Adds a new parameter to getFriends in Profile.php that allows the user to specify if the response should include friend requests or not. False by default.
• Adds a new function called removeFriend($id) to Profile.php that allows to reject a friends request or remove a friend (both actions use the same endpoint)