shared form styling and stacked modals

re: styling generalization (should make an issue for this)

[ ] use style snippets for spacing (padding, margin)
[ ] unify styling of NewTag, NewActivity, NewNote
[ ] (wip) buttons to open NewActivity, NewTask, NewNote in Today
[ ] redo modal system to properly handle stacking modals (needs revisit when we do modals with wrappers that aren't full-screen
[ ] invalidate activities query on new activity submission
[ ] pass default isTask to NewActivity and fix checkbox change handler to properly flip state on initial click

Seerden / track