Disables block gravity and makes it togglable (FS-89) (#50)

* Disables block gravity by default (FS-89)

* Combine these checks as Codacy ever so kindly suggested

src/main/resources/config.yml

@@ -226,6 +226,7 @@ allow:
   respawnanchors: false
   auto_tp: false
   auto_clear: false
+  gravity: false
 
 # Blocked commands:
 #