Don't block the main thread while running CliInterface jobs

Currently we freeze the GUI thread while running CliInterface jobs,
because there is a nested event loop in runProcess(),
which doesn't run anymore in a separate thread.

We can simply drop this event loop and rework the CliInterface logic,
such that the emit signal is not emitted anymore when runProcess() returns,
but in processFinished() instead.

This exposed a crash when closing the main window while a pending job was
running. The fix is simply to not emit finished() if the m_abortingOperation
flag is set.

BUG: 222392
FIXED-IN: 16.08.0

CCBUG: 193908

Differential Revision: D1510