Replace readable names by uuids in the readme, tests and examples

[rhamzeh]

For example here in the .NET SDK

var body = new ClientCheckRequest {
    User = "user:81684243-9356-4421-8fbf-a4f8d36aa31b",
    Relation = "writer",
    Object = "document:roadmap"
};

can be written as:

var body = new ClientCheckRequest {
    User = "user:81684243-9356-4421-8fbf-a4f8d36aa31b",
    Relation = "writer",
    Object = "document:9f81b5ba-cd00-450e-8127-3786c92aeab9"
};