KGet frameworks branch

[Wolfgang Bauer]

Hi all!

I spent some time during the last weeks on the KF5 port of kget to fix 
problems I noticed, e.g. opening the transfer history crashed, the bittorrent 
plugin wasn't built at all and needed some fixes to actually compile, disabled 
plugins disappeared from the settings, some incorrect QUrl usage that caused 
file:/xxx destinations being displayed and a folder hierarchy file:/xxx to be 
created, ...
I also ported it from KUniqueApplication to QApplication and KDBusService.

Review Requests are upcoming, although I assume it's fine to commit minor 
fixes directly (without review), right?

The only remaining major problem I'm still facing is that downloads fail to 
start if the multiseg plugin is enabled (which it is by default). I'll try to 
investigate and fix this too, but in the worst case it could just be disabled 
for the 17.12 release...
Otherwise it seems to work fine here with my local changes (with multiseg 
disabled and using the normal kio plugin).

So I'd like to ask: can we merge frameworks to master? AIUI this needs to be 
done before the dependency freeze tomorrow.
(my fixes so far don't add any new dependencies anyway, so it should not be a 
big problem if they are not committed yet)

PS, two differentials are here, if somebody wants to look at them (reviews 
would be nice of course ;-) ):
https://phabricator.kde.org/D8719
https://phabricator.kde.org/D8724

Kind Regards,
Wolfgang