Adding functionality to automatically add subject_id on opening the page.

Changes include:

By using this action tag, the target field is set as

<DAG_ID>-<FIRST_NAME_INTIAL><LAST_NAME_INITIAL><RECORD_ID>

If DAG ID is absent then the target value is set as
```
<FIRST_NAME_INTIAL><LAST_NAME_INITIAL><RECORD_ID>
```

Review steps:

[ ] Make sure that WARRIOR Specific Features is enabled in your project
[ ] Make sure that your project contains first_name and last_name fields
[ ] In the form that goes next these fields, add a new field (e.g. "Subject ID") with action tag @SUBJECT-ID
[ ] Create a new data entry and fill first & last name fields
[ ] Move forward to the next step and make sure you see a readonly Subject ID field containing a value that matches to the pattern described above
[ ] In another tab, configure WARRIOR module in order to switch first name and last name fields (just to test if configuration works)
[ ] Refresh form and make sure that the initials have been switched (e.g. JM becomes MJ)
[ ] Save & stay and make sure Subject ID is saved and still readonly
[ ] Make sure to test both DAG and non-DAG cases

ctsit / warrior_specific_features