refactoring of euphonic widgets and model

[mikibonacci]

As suggested by @AndresOrtegaGuerrero , we should refactor the euphonic widgets (the three tabs) to be only one, which can be adapted for each case by means of an attribute which describe the scope of the widget. For now this behaviour is implemented in Raman and IR widgets, not in euphonic ones.

This can greatly simplify readability, avoid code duplication (partially solved by inheritance but not very clearly), and probably help in solving some issue which euphonic produces when rendering (some data processing hangs and blocks the app).

• one model
• one widget
• update authors in the files