make getClientConfiguration type safe

TS type assertions need to be avoided.

The following trivial example demonstrates why

```
type Person = {
	name: string;
	isBad: boolean;
};

function makePerson(): Person {
	const p: Person = {name: 'whatever'} as Person
	p.isBad = false
	return p // theoretically we are now good, p is a Person
}
```

Should the type ever change though, TS will happily trot along

```
type Person = {
	name: string;
	isBad: boolean;
	omgHowCouldYou: number;
};

function makePerson(): Person {
	const p: Person = {name: 'whatever'} as Person
	p.isBad = true
	return p // p is *not* a Person, omgHowCouldYou is missing
}
```

But we pinky swore to the compiler that p is in fact a Person.
In other words, the types are now wrong and you will fail during
runtime.

server/server.ts

@@ -421,8 +421,10 @@ function indexRequest(req: Request, res: Response) {
 				throw err;
 			}
 
-			const config = getServerConfiguration() as IndexTemplateConfiguration;
-			config.cacheBust = Helper.getVersionCacheBust();
+			const config: IndexTemplateConfiguration = {
+				...getServerConfiguration(),
+				...{cacheBust: Helper.getVersionCacheBust()},
+			};
 
 			res.send(_.template(file)(config));
 		}
@@ -901,11 +903,7 @@ function getClientConfiguration(): ClientConfiguration {
 }
 
 function getServerConfiguration(): ServerConfiguration {
-	const config = _.clone(Config.values) as ServerConfiguration;
-
-	config.stylesheets = packages.getStylesheets();
-
-	return config;
+	return {...Config.values, ...{stylesheets: packages.getStylesheets()}};
 }
 
 function performAuthentication(this: Socket, data) {