feat: Timestaming with UTAG

[jerzyjamroz]

The timestamping can be used in two ways from now on:

• Timestaming with UTAG (new): import file evreventutag.db instead of evrevent.db. UTAG value is applied by writing into: "$(EN)-SP" record, the timestamp+UTAG is provided by $(EN)Cnt-I record (EPICS Base 7 or higher).
• Timestaming (legacy): import file evrevent.db and ignore evreventutag.db, the timestamp is provided by $(EN)Cnt-I record, so as it was before (legacy).

The solution is based on the:

1) Feedback from the epics core team:

• https://github.com/epics-base/epics-base/issues/442
• https://github.com/epics-base/epics-base/pull/397 2) Initial implementation and tests by @joaopaulosm: https://github.com/jerzyjamroz/mrfioc2/pull/5