Add missing timestamp indexes to migration, refs T805

Summary: Each of the database tables that have created and updated columns should also have indexes on those columns, this because of using these fields for sorting frequently, So adding the indexes in a new migration file.

Test Plan:
```
bin/phinx migrate -c application/phinx.php
```

After running the migration tool the indexes will appear in table structure when trying to run "desc table_name".

Reviewers: john.levermore, shadowhand

Reviewed By: shadowhand

Subscribers: rjmackay

Maniphest Tasks: T805

Differential Revision: https://phabricator.ushahidi.com/D393