On-device gdb is an exception, because the local installation
does not know about it.

In cases where binary 'wish' is not in PATH variable this could not be
started.

The cdb debugger factory claims to be able to run, yet returns 0 from
run(). Int that case do nothing.

Just some API cleanup

Task-number: QTCREATORBUG-2341 (en passant)
Reviewed-by: Alessandro Portale

Task-Number: QTCREATORBUG-2375

While it was set to 2 for most editors, some editors, like the .pro file
editor, set another document on the BaseTextEditor, which then did not
get its cursor width set.

Also removed a duplicated line.

Reviewed-by: dt

Reviewed-by: kh1

Adapt Qt4ProjectManager to use QMLOBSERVER instead of QMLINSPECTOR
(got changed in commit a10b2692)

This also obsoletes one class and one UI file.

Reviewed-by: Alessandro Portale

Reviewed-By: dt

We should restrict ourselves to calling all qml debugging support
observer, instead of mixing qml debugger / inspector / observer
interchangeably.