TREGO using batch trust regions

[khurram-ghani]

Related issue(s)/PRs: #773

Summary

This PR adds a TREGO implementation based on the new batch-trust-region classes and replaces the original TREGO TrustRegion implementation.

Existing notebook, unit tests and integration tests have been updated to use the new classes.

Fully backwards compatible: no

We have agreed that we don't need backwards compatibility -- see discussion below.

Previously, a TREGO rule was created like this:

rule = TrustRegion()

This will need to be replaced with the following:

rule = BatchTrustRegionBox(TREGOBox(search_space))

PR checklist

• The quality checks are all passing
• The bug case / new feature is covered by tests
• Any new features are well-documented (in docstrings or notebooks)

[hstojic]

this is quite neat! surprisingly small amount of changes :)

[hstojic]

I think this is great, but if we eliminate TREGO, this would break backward compatibility, right?
I think we should still do it...
@vpicheny ? @uri-granta ?

[vpicheny]

We don't need to be back-compatible so it's fine to use TREGOBox