Add notification type to onboarding sequence

[axu-1]

Add a screen asking for the user's notification type preferences and time. Similar to the settings page's design.
Refer to #108 and wait for that to be done first. The notification type screen must come after the period data gets inputted, but before the final "see you on that date" screen.
In fact, it may be useful to have it be on the same screen, like "see you on that date! how would you like us to remind you?"

See parent issue #116 for more details.