move module-based-service parameter types into service

This is in preparation for writing something that extracts them
into documentation.

user configurations now call config.system.service.foo.build { ...params }
instead of config.system.service.foo

the parameter type definitions themselves now move into the
config stanza of the module referencing the service

new helper function  liminix.callService

The only service moved so far is dnsmasq

tests/pppoe/configuration.nix

@@ -41,7 +41,7 @@ in rec {
     };
 
   services.dns =
-    config.system.service.dnsmasq {
+    config.system.service.dnsmasq.build {
       interface = services.lan4;
       ranges = ["192.168.19.10,192.168.19.253"];
       domain = "fake.liminix.org";