Deprecates the following attributes from ModuleSystem:
* replace_urls
* replace_course_urls
* replace_jump_to_id_urls
A new ReplaceURLService is created as replacement with a unified replace_urls method
Previously, dismissing one course update would disable all future
updates. But that feels a bit limiting.
Instead, these are the new rules:
- If the newest update has not been dismissed yet, it gets displayed.
- If the newest update has been dismissed, we display nothing.
- Editing the newest update will cause it to be displayed again.
- New updates get displayed, even if previous updates were dismissed.
This commit includes a light refactoring and addition of some utility
methods to help manage the above.
It also notes that the learning MFE does not use the "latest_update"
waffle option, which controls the labeling of the update message.
