Make QML code depend less on the `kcm` context property

It allows reusing components from org.kde.kcm module in other code which is not running in a KCM module. A marginal use-case, but a possible one. For example, according to lxr1 search, the Timer applet is the only applet that uses those controls, but still it shouldn't spam logs with meaningless 'undefined reference' messages, since mostly (without going into applet's general usability concerns) it seems to be working perfectly fine.