Give time to external unpackers to uncompress very big files. Show more error messages

Notes:

1. A method in order to {check if the process is running} was used like the one in https://doc.qt.io/qt-5/qprocess.html:

    if (!builder.waitForFinished())
        qDebug() << "Make failed:" << builder.errorString();
    else
        qDebug() << "Make output:" << builder.readAll();

2. An

    error(KIO::ERR_SLAVE_DEFINED, i18n("After [...]

line was utilized, which is analogous to the

    error(KIO::ERR_SLAVE_DEFINED, i18n("Copying to mtp slaves is still under development!"));

line in https://github.com/KDE/kio-stash/blob/master/src/ioslave/ioslave.cpp

3. A proc.waitForFinished(-1); line was used, like two similar ones in kmountman.cpp.

GUI: A new error message can be seen by the user.

FIXED: [ 433294 ] Gibberish error when extracting large file from zip archive

BUG: 433294

Revision: !44 (merged)