make event detail buttons into actual button elements
make event detail buttons into actual button elements

fixes CNVS-25667

test plan
- create an event on the calendar
- click the event
- ensure that the "Delete" and "Edit" buttons on the popup are
 buttons and behave like them (space or enter activates them)

- as a teacher, create an appointment group
- as a student, select the appointment on the calendar
- ensure the "Reserve" button is a button and behaves like one
- reserve the appointment slot
- reload the calendar
- select the appointment on the calendar
- ensure the "Un-reserve" button is a button and behaves like one
- reserve the appointment slot
- as the teacher, click the appointment on the calendar
- ensure the "Message students" button is a button and behaves
 like one

Change-Id: I10cfd0678ce0c5a5a807a1cc32453374d0085f8c
Reviewed-on: https://gerrit.instructure.com/70205
Reviewed-by: Aaron Cannon <25919c673621c006b735dcd5a28df63325948e2b@instructure.com>
Product-Review: Aaron Cannon <25919c673621c006b735dcd5a28df63325948e2b@instructure.com>
Tested-by: Jenkins
Reviewed-by: Matthew Wheeler <ce71fbafda91d6c8f12582e1837687d5fe592dd9@instructure.com>
QA-Review: Heath Hales <8ca81b68c7e2592ac614bd07f22fcc735ca55f93@instructure.com>
QA-Review: Adrian Russell <5867b55c34ec258a06bcc4d9b6dbda2c79313b40@instructure.com>

grahamb/canvas-lms,HotChalk/canvas-lms,venturehive/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,roxolan/canvas-lms,matematikk-mooc/canvas-lms,fronteerio/canvas-lms,roxolan/canvas-lms,HotChalk/canvas-lms,grahamb/canvas-lms,matematikk-mooc/canvas-lms,sfu/canvas-lms,redconfetti/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,SwinburneOnline/canvas-lms,sfu/canvas-lms,SwinburneOnline/canvas-lms,redconfetti/canvas-lms,SwinburneOnline/canvas-lms,sfu/canvas-lms,fronteerio/canvas-lms,djbender/canvas-lms,grahamb/canvas-lms,redconfetti/canvas-lms,dgynn/canvas-lms,dgynn/canvas-lms,redconfetti/canvas-lms,venturehive/canvas-lms,matematikk-mooc/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,grahamb/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,fronteerio/canvas-lms,instructure/canvas-lms,matematikk-mooc/canvas-lms,djbender/canvas-lms,fronteerio/canvas-lms,HotChalk/canvas-lms,venturehive/canvas-lms,instructure/canvas-lms,dgynn/canvas-lms,roxolan/canvas-lms,instructure/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,grahamb/canvas-lms,HotChalk/canvas-lms,dgynn/canvas-lms,SwinburneOnline/canvas-lms,roxolan/canvas-lms