Refactor UI for Multiple Offerings and Recurring Events

[ojmakinde]

This issue is a break-up of #1335.

Recurring events (or repeating events) are simply multiple offerings that have the same title and occur at the same time every week. Since they are similar, merging the process of creating multiple or repeating events should be similar. The current plan is to:

• Use the same modal for repeating and multiple offerings.
• After creating multiple repeating, have the modal simply add "Week X" to the number of repeating events
• Merge the logic for saving repeating and multiple offerings.