system_service patch for D7

So, heyrocker suggested having a working version of current services module before thinking in a refactoring. IMO this is an extra job for now, but in the end would provide backward compat. for old services implementation, so here we go. It is not my intention to make regression test for any function in the module, but for services' test module I found required to know if each xxxx_service is working as expected.

I didn't review all the code, just make sure tests pass.