[feature] s3-loading-icon

**Purpose**
- Addresses [#1187](https://github.com/CenterForOpenScience/openscienceframework.org/issues/1187)
- Currently, if a user authorizes the Amazon S3 addon via a project settings page (i.e. when ```node_has_auth``` and ```user_has_auth``` are both ```False```) the user is told to wait and refresh the page after importing their access key and secret key.

**Changes**
- This PR adds a timeout to refresh the page 3 seconds after the authorization finishes. It also displays the text ```S3 access keys loading...``` during the timeout so the user knows to wait. After speaking with @chrisseto, this process should always take between 2 and 3 seconds (no matter the amount of buckets in the user's S3 account) so a three second timeout should be sufficient, and has worked every time I have tested it.

**Side Effects**
- If ```bucket_list``` is still ```None``` after the three second timeout, then an error message (```Error loading S3 access keys. Please refresh the page.```) will be displayed.