Scroll to file on search or add

Fixes the following cases:
1) Type a file name in the search box, click on the result in the dropdown (the file must be in a different dir). It will open the matching directory and scroll there.

2) Activity app, when clicking on a file, it will go to the files app and scroll to it.

3) Create a new file or folder with the menu, it will scroll to that file.

Note that the search and activity apps simply use the "scrollto" URL argument which is what triggers the scrolling.

Please review and test @th3fallen @butonic @icewind1991 @owncloud/designers 

Fixes https://github.com/owncloud/core/issues/10737