luci-mod-status: move index acl into own file

The ACL file luci-mod-status.json is already quite long.
It is also a separate menu item in LuCI, so in my view it makes sense to
move it to a separate file. An additional positive effect is that the
file then becomes clearer.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>