Implement Message Activities Feature, Fixes T450

Summary:
- Fix the broken Activity link so when you click on it it shows the hidden content.
- Replace the dummy content with the actual activity content.
- When there is no activity on a message, replace that with an empty view saying, No activity on this message

Test Plan:
- Go to #messages
- Click on `Activity`
- See posts details display
- Otherwise see `No activity on this message`

Reviewers: shadowhand, rjmackay

Reviewed By: shadowhand, rjmackay

Subscribers: seth, srutto, lkamau

Projects: #ushahidi_platform

Maniphest Tasks: T450

Differential Revision: https://phabricator.ushahidi.com/D242