Changed to asynchronous download in converter/webpricequote

Using KIO::file_copy now.

The code in dialogs/kequitypriceupdatedlg was ideal to code this feature.
The first download is triggered by slotUpdateAllClicked. Then the next
downloads are trigered by signals from WebPriceQuote. This makes the
ideal possibility to create assynchronous transfers as getting back to
slotUpdateAllClicked immidietly after starting the job haven't broke
anything.

The original review request was based on master which is qt4 based.
Christian David adopted the changes to KF5 and Qt5.

BUG: 275004
FIXED-IN: 5.0
CCMAIL: Artur Puzio <cytadela88@gmail.com>
REVIEW: 126882