Fix feed endpoint issues

What does this MR do?

Update the Feed endpoint in the given ways:

• Hide user content if user has not yet posted.
• Add hasUserPosted field in returned JSON.
• Only fetch friend's dailies for the given question ID.

Relevant screenshots

(Add any relevant screenshots of MR's functionality)

Testing

• Wipe all Dailies for the current question.
• Post a Daily with the userId of the main user's friend.
• Get the feed of the main user.
• The content of the dailies should be an empty string.
• The hasUserPosted field should be false.
• Post a Daily with the userId of the main user.
• The content of the dailies should not be an empty string.
• The hasUserPosted field should be true.

Relevant issues

Closes #31 (closed). Closes #32 (closed).