Sent the file path in the load method instead in the loader constructor

[zazoomauro]

Instead of loading the service configuration file in the FileLoader constructor load the file directly in the load method.

import {ContainerBuilder, YamlFileLoader} from 'node-dependency-injection'

let container = new ContainerBuilder()
let loader = new YamlFileLoader(container)
loader.load('services.yml')

1. Deprecate the second parameter usage in the constructor. (throw a deprecated warning if the second parameter is sent)
2. Enable an optional parameter in the load method (throw a deprecated warning if the parameter is not set)