Rename PlayerInstance to Zone

...inContentPlayer/src/main/resources/view/ZoneSettings.fxml

.../de/tobias/playpad/plugin/content/ContentPluginMain.scala

.../playpad/plugin/content/pad/ContentPlayerPadContent.scala

...t/pad/ContentPlayerPadContentSettingsViewController.scala

...d/plugin/content/player/ContentPlayerViewController.scala

...bias/playpad/plugin/content/player/MediaPlayerStack.scala

...s/playpad/plugin/content/settings/ZoneConfiguration.scala

.../plugin/content/settings/ZoneSettingsViewController.scala