[ENG] Rename group_trial_status_* → trial_status_*

Rename a few of the trial status widget/popover files to better match what they provide or what they test.

Before	After
ee/app/assets/…/group_trial_status_widget_and_popover.js	…/init_trial_status_widget_and_popover.js
ee/spec/…/group_trial_status_popover_spec.js	…/trial_status_popover_spec.js
ee/spec/…/__snapshots__/group_trial_status_popover_spec.js.snap	…/trial_status_popover_spec.js.snap
ee/spec/…/group_trial_status_widget_spec.js	…/trial_status_widget_spec.js
ee/spec/…/__snapshots__/group_trial_status_widget_spec.js.snap	…/trial_status_widget_spec.js.snap

And update the reference to the newly-renamed init_trial_status_widget_and_popover.js file in ee/app/assets/javascripts/pages/groups/index.js.