Display deprecated status in all application wrappers

Applications can be marked deprecated with AddDocTag(Tags::Deprecated); but this is not really visible for applications users. Therefore we should display the deprecation status clearly in all wrappers:

• In cli: Display a clear message at the beginning of documentation display, and also a WARNING log when the app starts
• In gui: Add red DEPRECATED text box somewhere
• In qgis-plugin: display the info somehow
• In cookbook documentation script generation: add a deprecation string at the beginning of app documentation
• In python API, what can we do ?