Python Editor Programmable Filter Integration

This MR adds a new feature that links the current programmable filter scripts to the python editor. More precisely, it, instead of opening it in a sole window, opens it in the python editor when clicking the pop button in the editor.

The old pqPopoutWidget is not used anymore, an tests have been modified accordingly.

The implementation proposed here provide flexibility for future developments: the new class pqTextLinker acts as a generic class that can links any QTextEdit like object. Anyone who wants to link an QTextEdit like object should derive from pqLinkedInterface and implement the abstract functions.