Improve kdeconnect_add_plugin macro

The macro arguments are mostly redundant. The only information needed is a name. Make the macro only take a name and deduce the rest from it.

This allows to add further things to the macro that need the plugin name, for example automatic creation of debug categories (which I want to do in a later patch)

sendnotificationsplugin is a bit special since it used a different json file. Lacking a proper solution for this I'm keeping the old macro as kdeconnect_add_plugin_old