Close #103 Filter running time entry by owner_id

[EliuX]

This does multiple things:

• It starts allowing any subdomain of in b2clogin.com in the claim iss of the JWT the API requires.
• In the running endpoint, it filters the running endpoint by the owner_id.
• It verifies through a test that the string representations of the UTC datetime entries, e.g. the start_date and end_date in the time entries, can be compared effectively.
• Adds documentation in the README about how to use the JWT to authenticate.