Add last_updated for all tables

[amplifi]

Currently, the platform only records last_updated datestamps for organizations and projects. By adding a last_updated datestamp column to all platform tables, we will be able to:

• leverage the availability of this data for more efficient indexing
• offer the capability to search/filter project data by date added
• add user dashboard features like displaying events since last login
• provide our partners with a chronological audit of data actions
• enhance platform security by supporting action-based alerts
• ...

The last_updated column should be initialized to a default value that is distinct from the range of actual values, such as 01/01/2016 00:00:00, to make it easy to identify rows that have or have not been modified since implementing this change. The last_updated values for each table should be managed via PostgreSQL trigger, which eliminates the need for any platform code changes and results in a more reliable implementation, as the database will be solely responsible for setting and modifying the value (particularly in the case of platform action failure, rollback, transaction queuing, etc).

[amplifi]

Additional requirements for update + username log: https://devwiki.corp.cadasta.org/History%20Log