[kdenlive] Online resources fix version 2

[Roger Morton]

I have submitted a patch (saw that reviewboard posted it to this list)
that makes the online resources functionality authenticate with
freesound to allow users to download high quality audio.  Sorry
Vincent - I could not figure out how to get the freesound login to
work without using a QWebView object to display the freesound web
page. I did try using a QTextBrowser
 for this purpose but it responds to the URL that is used to connect with
 "No document for https://www.freesound.org/apiv2/oauth2/authorize/?blah blah"

The use of QWebView adds a dependancy on the KF5WebKit to kdenlive.
Need install libkf5webkit5-dev package on ubuntu to build it
might only need libkf5webkit5 to run it.

I have documented how it works here:
https://userbase.kde.org/Kdenlive/Manual/Project_Menu/Online_Resources#Freesound_Audio_Library_-_Future_version