Allow users to display certain buckets only

[kdzhao]

For any reasonable sized environment, the aws s3 ls will return a large number of bucket names, and most of them are not related to the user's interests. It will be great to have a configuration somewhere, that filter out the unrelated bucket names and only display the ones users want.

• Let's make sure users know this only filters out in the UI, not by underlying permission.
• An example is to check if there is a config file under current user's home folder. If yes, use a predefined parameter in that file to filter.

[rabernat]

This appears to be a duplicate of #18.