Schema ID is not validated on resource creation

[icamys]

I've noticed that if the client sends a resource creation request with an invalid schema, it reaches the HTTP handler:

{
    "schemas":["urn:ietf:params:scim:invalid:schema"],
    "userName":"example@domain.com"
}

Considering that schema and its extensions are attached to the resource on server creation, should any schema name validation be present? If so, then I'll be happy to implement this validation.

[q-uint]

We should indeed check this and not just ignore it, this is a bug.
By default we do ignore all fields that are not defined within the schema, but schemas is part of each schema be default.

[icamys]

@q-uint I've prepared a fix for this. Is it ok if I create a PR after #169 is merged?