Replace mesecons by dedicated submodule

The currently packed version seems to have a problem with placing table lamps,
but the version now included as a submodule does not.

Maybe this should be reported to the package maintainer?

.gitmodules

@@ -100,3 +100,6 @@
 [submodule "anvil"]
 	path = anvil
 	url = https://github.com/minetest-mods/anvil
+[submodule "mesecons"]
+	path = mesecons
+	url = https://github.com/minetest-mods/mesecons

README.md

@@ -19,7 +19,6 @@ sudo apt install                    \
      minetest-mod-currency          \
      minetest-mod-infinite-chest    \
      minetest-mod-intllib           \
-     minetest-mod-mesecons          \
      minetest-mod-torches           \
      minetest-mod-unified-inventory
 ```

mesecons

@@ -0,0 +1 @@
+Subproject commit f5c3f798be94cc95b93e5fe480f537dc41d6f350