AppletConfiguration: Only set config keys that exist in page
This avoids errors when we attempt to set all config keys, some of which aren't properties in config pages.
e.g., switching to Weather Report's about page:
plasmashell[955110]: file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/configuration/AboutPlugin.qml: Setting initial properties failed: AboutPlugin does not have a property called cfg_pressureUnit
plasmashell[955110]: file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/configuration/AboutPlugin.qml: Setting initial properties failed: AboutPlugin does not have a property called cfg_pressureUnitDefault
plasmashell[955110]: file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/configuration/AboutPlugin.qml: Setting initial properties failed: AboutPlugin does not have a property called cfg_showHumidityInTooltip
plasmashell[955110]: file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/configuration/AboutPlugin.qml: Setting initial properties failed: AboutPlugin does not have a property called cfg_showHumidityInTooltipDefault
plasmashell[955110]: file:///usr/share/plasma/shells/org.kde.plasma.desktop/contents/configuration/AboutPlugin.qml: Setting initial properties failed: AboutPlugin does not have a property called cfg_showPressureInTooltip
… (it goes on, for much longer)
Edited by Oliver Beard