Database column name "study_id" is misleading

[alena456]

Description

The field name "study_id" which is used for identification of study participants is misleading and should be renamed. It sould indicate that this value represents a subject identifier.

Study systems usually reference the following terms:

• SubjectID (integer) as database reference for table relations
• SubjectNumber (text) for a generated or assigned identifier for study participants that is used to identify subjects within a study center

ToDo

The name of the field should be updated in the code and all relating documentation.

[alena456]

I propose to use "subject_id" as reference in the database and code to have one consistent name.

[alena456]

@lenzch Should we also change the reference "AppId" used for the cTransfer object to "SubjectID" in order to make the value more relatable?

[alena456]

@lenzch do you have a preference regarding the naming of the corresponding database table? It is currently called "STUDYUSER". I would propose to rename it to "STUDYPARTICIPANT".
Also I would like to rename the "user" route accordingly to "/subject" or "/participant".

[lenzch]

@alena456 I think naming the table "STUDYPARTICIPANT" and the primary key "subject_id" is fine.
And the route should be named "/participant". Thank you.

[alena456]

Merged changes after validation #7