Support custom data fields in scheduler and emitters

[btjanaka]

Description

This PR makes it possible to pass in custom data to schedulers and emitters. For instance, one can call

scheduler.tell(objective, measures, my_data=[1,2,3], my_other_data=[4,5,6])

The same applies for tell_dqd, and also for emitter methods.

TODO

• Update scheduler signatures
• Update emitter signatures
• Miscellaneous edits to ArrayStore and archives
• Write scheduler test

Questions

Status

• I have read the guidelines in
  CONTRIBUTING.md
• I have formatted my code using yapf
• I have tested my code by running pytest
• I have linted my code with pylint
• I have added a one-line description of my change to the changelog in
  HISTORY.md
• This PR is ready to go