Re-implement settings system:

Settings can now be retrieved by mesecon.setting(<name>, <default>) and can be modified without
editing the source code by adding the setting to minetest.conf
For instance, you can add mesecon.blinky_plant_interval = 0.5 to minetest.conf in order to
increase the blinking speed.
Rewrite the blinky plant with nodetimers.
Fixes #161

mesecons_luacontroller/init.lua

@@ -201,7 +201,8 @@ local create_environment = function(pos, mem, event)
 			tostring = tostring,
 			tonumber = tonumber,
 			heat = minetest.get_meta(pos):get_int("heat"),
-			heat_max = OVERHEAT_MAX,
+			-- overheat_max Unit: actions per second, checks are every 1 second
+			heat_max = mesecon.setting("overheat_max", 20),
 			string = {
 				byte = string.byte,
 				char = string.char,