Added spinners in share dropdown

Added spinners for the following actions:
- adding user
- removing user
- changing password
- toggling allowing upload
- setting a password
- autocomplete

Fixes https://github.com/owncloud/core/issues/11154 by adding spinners so the user knows that the system is currently working. (it does not fix the cause of the slowness)

Note: if you close the dropdown while it's working and reopen it will not reappear. I can't add a spinner at this time without invasive changes that are likely to break apps.

@owncloud/designers @ser72 @schiesbn @icewind1991 @th3fallen