Adding option to detect previous event based on a date field

[tbembersimeao]

Review steps:

• Check additions on README and make sure they make sense
• Enable chronological previous event detection in a longitudinal project of your choice
• Make sure your project has at least one field containing @DEFAULT-FROM-PREVIOUS-EVENT action tag
• Complete events in a non linear fashion. For each new event you fill out, make sure the action tagged field is auto populated with the value from the last chronological event
• Make sure there are no regressions on the default functionality
• [DEVELOPERS ONLY] make sure redcap_log_event db table is indexed after enabling (or upgrading) the module

[pbchase]

This is so cool. I love this feature. It feels like magic. definitely merging.