django: move django* packages under django submenu

This changes the python[3]-django dependencies in packages to be
non-selecting, and adds an MDEPENDS line so that the *-src packages get
placed inside the django menu as well.

Added MENU:= to the src-package definitions in python[3]-package.mk,
so it does not import that setting from the binary package.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>
(cherry-picked from commit 90527d75af)

lang/python/python-package.mk

@@ -45,6 +45,7 @@ define PyPackage
     EXTRA_DEPENDS:=
     TITLE+= (sources)
     USERID:=
+    MENU:=
   endef
 
   define Package/$(1)-src/description