add support to submit files hosted by multiple providers during same session

[ritalui]

Currently, a user can be authenticated by Google multiple times using multiple credentials (associated with multiple Google accounts). Table provider_auths supports this functionality. Each authentication results in an entry in the table, asociated with user_id, provider_id and uid (provider's user id). As a result, if a user has two Google accounts and is authenticated by Google twice using two different credentials, there will be two authentications in the table with the same user_id and provider_id, but different uid's.

However, currently, there is no code for file submission from different Google accounts during the same login session. Code needs to be added to display provider's uids to the user during file submission, so that the user can indicate with which uid (provider account) the file to be submitted is associated.

Note: The current code uses the access_token from the first authentication entry found with matching current_user.id to formulate the API request. There is a mismatch of access_token and uid if the file to be submitted is not associated with the uid in the first authentication entry found.