[adams2019] Restructure autoscheduler + add timer

[rootjalex]

Adds caching of features and schedule enumerations to the adams2019 autoscheduler. Backported from @aekul 's autoscheduler work.

On my machine, I see a x2 speedup on the time needed to autoschedule lens blur and local laplacian, about a x1.5 speedup for resnet50, and anywhere between x1-1.5 for other pipelines (caching is only useful for larger pipelines, it has little to no effect on smaller pipelines).
This PR is now just a restructuring + addition of a timer to the adams2019 autoscheduler, to allow for the addition of caching.

[steven-johnson]

Buildbots are green (ignoring the buildbot-beta); looks ready to be reviewed.

[abadams]

This is large and hard to review. It looks like there are two things here - a refactor of the autoscheduler into more files, and adding caching. Is it possible to disentangle them into separate PRs (e.g. by deleting everything caching related from this PR, and then reintroducing it in another?). I can't tell what's moved code and what's new.

[rootjalex]

@abadams This PR should now just be restructuring (+ the addition of the timer, but I can remove that and put it in the caching PR if necessary).

[abadams]

lgtm with one final suggested change.

[abadams]

Thanks, you are good to merge once the bots are all green.

[rootjalex]

Failures look unrelated to the autoscheduler, @steven-johnson can you confirm?

[steven-johnson]

Failures are unrelated, OK to land