Fix types and required fields

[mdbenito]

This PR adds:

• Missing types in Department (label and universal_id)
• Missing id poperty in Team (id) and type (name is a string)
• Missing property in Absence (comment, string)
• Required properties in ShortEmployee (attributes.id.value)
• Required properties in Absence (many, all part of responses)
• Required properties in Employee (id.value)
• Required property in Time-off type (id)

Every change is isolated in its own commit so it should be easy to revert them, should they not be desired. I believe none of the changes should break client code since they either add fields that are part of the responses, fix types, or specify that a response will always contain them.

[mdbenito]

Any chance this can be merged?