Integrate a way to easily use user-submitted datasets

[JunodCharlie]

Users may need to use their own datasets alongside the ones provided by onTime via the Dataset class. In particular, there needs to be an easy way to submit both user and ontime datasets together for benchmarking.

To do:

• Identify the need for a dedicated data structure/class
• Implement said data structure if needed
• Write a doc example showing how to use user datasets alongside ontime datasets