KCModuleData: Add auxiliaryAction and isRelevant

This lets a KCM provide additional features to the user without having to the enter the KCM:

• whether it is relevant in the current environment, e.g. whether the device type, such as a touchscreen or graphics tablet, is availbale in the first place
• an auxiliary action, that can either be a button to e.g. pair a new device, or a switch to toggle a feature, e.g. turn on/off Bluetooth

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I could think of additional features, like a dynamic tooltip, e.g. “1 device paired”