Debugger: Make Python's subprocess dependency optional

This is only used to display array data using gnuplot.

Task-Number: QTCREATORBUG-10205
Change-Id: I9a9173860e4f6d37f475c7f101c0e85d104ab10a
Reviewed-by: hjk <hjk121@nokiamail.com>
Debugger: Fix QList<QStringList> dumper with Qt 5

QStringList is movable in Qt 5.

Task-number: QTCREATORBUG-10211
Change-Id: I6b94acd37bbf8ca165960c50fd3da81408ccbb1b
Reviewed-by: David Schulz <david.schulz@digia.com>