New defaults for Unscented and Infinite-time algorithms

[odunbar]

Issue

Some of the defaults can be updated to be the latest configuration.

• We have suitable evidence that Unscented and TransformUnscented can use acceleration and it is beneficial - therefore making a good default
• We should note infinite-time algorithms [Inversion(prior), TransformInversion(prior) , Unscented, and others, do not have a "special" time T=1 at which they should be terminated early. Therefore the final time should be extended.
• impose_prior = true is our most common Unscented and TransformUnscented setting and so should be made a default.

Suggested solution:

• Add NesterovAccelerator(), (ekp default) and change impose_prior=true (uki/utki default) for Unscented and TransformUnscented variants
• Replace DataMisfitController(terminate_at=1) with DataMisfitController(terminate_at=1e8) for infinite-time algorithms