D5160: Set implicit size from source size for image/SVG URL sources.

[Eike Hein]

hein added a dependent revision: D5162: Port custom image mode to IconItem..

REPOSITORY
  R242 Plasma Framework (Library)

REVISION DETAIL
  https://phabricator.kde.org/D5160

To: hein, #plasma, mart, davidedmundson
Cc: plasma-devel, #frameworks, progwolff, lesliezhai, ali-mohamed, 
jensreuterberg, abetts, sebas, apol