Add function dropTimestamps()

Function to quickly drop the timestamps columns on a database table.

Signed-off-by: Dries Vints <dries.vints@gmail.com>
Add unit tests for dropTimestamps() function

Signed-off-by: Dries Vints <dries.vints@gmail.com>
Merge pull request #672 from driesvints/dv/drop-timestamps-function

Add dropTimestamps() function on Schema creator