Add extension points on Data for customizing Connectable behavior.

[mikeurbach]

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• Feature (or new API)

Desired Merge Strategy

• Squash: The PR will be squashed and merged (choose this if you have no preference).

Release Notes

The user can override these methods to customize how their Data applies waive, squeeze, and exclude in its Connectable.

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
• Did you mark the proper milestone (Bug fix: 3.6.x, 5.x, or 6.x depending on impact, API modification or big change: 7.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you do one of the following when ready to merge:
  • Squash: You/ the contributor Enable auto-merge (squash), clean up the commit message, and label with Please Merge.
  • Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.

[jackkoenig]

I don't think this works hierarchically, see comments.

[jackkoenig]

Generally LGTM assuming there isn't too much of a performance penalty (I think it's probably okay). Nice tests!

[jackkoenig]

LGTM one minor comment about possibly unused imports