feat(HttpLoader): make prefix & suffix public to be set dynamically

This allows developers to update the path where the translation files are loaded from. It might be possible that this path is some kind of configuration option within the application.

src/http-loader.ts

@@ -3,7 +3,7 @@ import {TranslateLoader} from "@ngx-translate/core";
 import "rxjs/add/operator/map";
 
 export class TranslateHttpLoader implements TranslateLoader {
-    constructor(private http: HttpClient, private prefix: string = "/assets/i18n/", private suffix: string = ".json") {}
+    constructor(private http: HttpClient, public prefix: string = "/assets/i18n/", public suffix: string = ".json") {}
 
     /**
      * Gets the translations from the server