Replace OC.Router.generate() with OC.generateUrl()

This fully removes the routes.json call on every page reload which has a real bad impact on the overall performance.

All ajax call using OC.Router.generate() have to wait until routes.json has returned and the routes are ready to be used. This can take seconds!

In addition I have seen routes.json having a payload of 23 KB.

This is all so unnecessary!

The replacement code will look like this:
```javascript
	download_url = OC.generateUrl(
		'apps/files/download{file}',
		{ file: $('#dir').val()+'/'+name });
```

Note that all app routes on the server start with ````apps/```` even if the app is installed in a different app folder.

I suggest to backport OC.generateUrl() to stable6 as well - devs can then modify their apps to run in oc6 and oc7+

@butonic @bantu @karlitschek @icewind1991 @PVince81 

refs #7307