Hotfix/uniform addon behavior

# Purpose
Make messages and behaviors more uniform across third-party storage add-ons.

# Changes
* Use consistent language on pre-registration hook for Dropbox, Figshare, S3, Dataverse
* Disable configuration copy on S3
* Update language in add-on capabilities modal

# Side effects
None expected

Note: I left the GitHub add-on as-is, since its registration logic is pretty simple, but we can skip that too.

Resolves https://github.com/CenterForOpenScience/osf.io/issues/1428