[qmp-system] Grant qMp full access to configuration files

LuCI recently implemented ACL for RPCD. This commit allows qMp LuCI
pages to have full access to configuration files in /etc/config.

It is meant to be a quick fix for #480, hoping for a proper solution
to be implemented.
Signed-off-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>

packages/qmp-system/files/usr/share/rpcd/acl.d/qmp-system.json

+{
+        "qmp-system": {
+                "description": "Grant qMp full access to UCI configuration files, legacy-style",
+                "read": {
+                        "uci": [ "*" ]
+                },
+                "write": {
+                        "uci": [ "*" ]
+                }
+        }
+}