DownloadedVideos: Use ViewPlaceholder instead of custom Label
DownloadedVideos: Use ViewPlaceholder instead of custom Label

Since Silica offers a ready to use element to inform the user the view
is empty let's use it instead of a custom element.

Signed-off-by: Peter Tworek <45f11722e542fe61db2d07ffa14ae9c3e4cb552a@gmail.com>

RobertMe/sailfish-ytplayer,tworaz/sailfish-ytplayer,RobertMe/sailfish-ytplayer,tworaz/sailfish-ytplayer,tworaz/sailfish-ytplayer,RobertMe/sailfish-ytplayer,RobertMe/sailfish-ytplayer,tworaz/sailfish-ytplayer,RobertMe/sailfish-ytplayer,tworaz/sailfish-ytplayer