gnu: kdenlive: Add missing dependencies.

This allows to browse the file-system using kdenlive's own file-chooser.

* gnu/packages/kde.scm (kdenlive)
[native-inputs]: Add pkg-config.
[inputs]: Add purpose and qtwebkit.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

gnu/packages/kde.scm

@@ -152,6 +152,7 @@ (define-public kdenlive
       (build-system cmake-build-system)
       (native-inputs
        `(("extra-cmake-modules" ,extra-cmake-modules)
+         ("pkg-config" ,pkg-config)
          ("qttools" ,qttools)))
       (inputs
        `(("shared-mime-info" ,shared-mime-info)
@@ -179,6 +180,8 @@ (define-public kdenlive
          ("qtquickcontrols2" ,qtquickcontrols2)
          ("kiconthemes" ,kiconthemes)
          ("breeze" ,breeze)
+         ("purpose" ,purpose)
+         ("qtwebkit" ,qtwebkit)
          ("qtgraphicaleffects" ,qtgraphicaleffects)
          ("kplotting" ,kplotting)))
       (arguments