Merge scheduler page and schedules page
This diff makes the scheduler page and the schedules-for-a-repository page use the same UI. The only difference is that the scheduler page is not repository-scoped.
Both pages show a list of schedules and a list of unloadable schedules. The scheduler page groups the schedules by repository.
In particular there are no longer any prompts to reconcile. The only reconcile-like experience you have now is the 'delete a now-unloadable schedule' experience.
Load a repo with two repositories, visit scheduler page and schedules page for each repository
Turn some schedules on and off, leave some on
Remove a running schedule from the codebase
Visit scheduler page and schedules page for both repos again, verify you can turn off the no longer existant schedule
Load dagit with empty workspace, see all running schedules available on scheduler page to turn off
Reviewers: sashank, dish, alangenfeld, prha
Reviewed By: sashank
Differential Revision: https://dagster.phacility.com/D5139