Fixed issue with notification dropdown not updating active
## What does this MR do?
This fixes an issue where the notification dropdown wouldn't correctly update the selected notification type in the dropdown. I've also added a spinner to show the action is happening & removed the flash message for success.
## What are the relevant issue numbers?
Closes#18480
## Screenshots (if relevant)

See merge request !4615
Refs dropdown is now loaded async
## What does this MR do?
The refs dropdown is loaded async so not to block the page.
## What are the relevant issue numbers?
Part of #18202
## Screenshots (if relevant)

See merge request !4508
Implement custom notification level options


part of #12758
See merge request !4389
* visiting project will create notification setting if missing
* change notification setting per project even without membership
* use notification settings instead of membership on profile page
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
* more focus for description and stars/forks
* rename activity -> to project tab
* put activity under tab: prepare place for README tab
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>