[mesecons] Add NOR and OR gates, and documentation

mods/mesecons/mesecons_detector/doc/nodedetector/description.html

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+The node detector is a receptor. It changes its state when either any node
+or a specific node is detected. Right-click it to set a nodename to scan for.
+It can also receive digiline signals. You can either send "GET" and it will
+respond with the detected nodename or you can send any other string and it will
+set this string as the node to scan for.
+Nodenames must include the mod they reside in, so for instance default:dirt, not just dirt.

mods/mesecons/mesecons_detector/doc/objectdetector/description.html

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+The object detector is a receptor. It changes its state when a player approaches.
+Right-click it to set a name to scan for.
+It can also receive digiline signals which are the name to scan for on the specified channel in the right-click menu.