Make starkde wait for drkonqi in a configurable way

By default, startkde still waits for remaining drkonqis with 15mins
timeout during the logout/shutdown procedure.

Run the following commands to configure that behavior :

    $ kwriteconfig --file startkderc --group WaitForDrKonqi --key Enabled false
    $ kwriteconfig --file startkderc --group WaitForDrKonqi --key Timeout 900

There is no GUI yet, so they are hidden options.

CCBUG: 126073