Clarify (replace) IfTrue in FlowControlType

[nsenave]

Analog to #80

TLDR: current modelling of this property is a bit flawed, make this cleaner in Pogues-Model in easy, but has quite a heavy impact.

Currently, FlowControlType (filter objects) has an IfTrue property, which is a string containing two identifiers, concatenated with a -, these two identifiers being the "first member" and the "last member" of the filter.

Example: a filter that starts on component with id "id1" and finishing at component "id3" would have:

"IfTrue": "id1-id3"

This modeling should be replaced by something cleaner.

Proposal

Backward compatible manner (to avoid clashes with existing questionnaires);

• add two new properties (proposal: "beginMember" and "endMember") in the FlowControlType object
• keep the "IfTrue", and mark it as deprecated if possible
• remove the "IfTrue" property and use the new modelling in Pogues front app
• adapt code in clients of the Pogues-Model lib / "Pogues-Model" files (see list below) in a backward compatible manner (accept either new or old property)

... and completely remove the "IfTrue" later on (when there will remain few questionnaires with this property)

📋 Clients that would have to make some changes:

• Eno (Pogues -> DDI)
• Pogues-Back-Office (on the composition feature, but maybe not only)