backend: fcgi_analyse() only supported with python controllers - add generic mode

[RoboSparrow]

The frontend for a generic survey (no python or business logic) would currently error out when trying to fetch an analysis

• current: fcgi_analyse() => get_analysis() => python analyse_* hooks
• proposed: fcgi_analyse() => get_analysis_generic()

since the generic mode is a simple sequence of questions the analysis cannot have business logic an only be a list of all answers in json. This is still useful for the frontend user to have.

[RoboSparrow]

analysis: generic placeholder skeleton implemented, currently only returning a static JSON string