plasmoid: only make active if we're a laptop

Screen layouts rarely change for desktop systems, making this feature unnecessary there. So for the multi-screen case, ler's only make the applet active if we're a laptop, where screens tend to be more transient and there's a higher likelihood of it being useful. Laptops that are docked 100% of the time are a rarer use case, and not easily detectable, so for those, users can manually disable this applet if they find that it annoys them.

@teams/usability @broulik @apol

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