fix #894 console hang with large number of files

There are two issues causing the browser to hang (busy).   

First, items are push one-by-one to ko.observable, this causes the UI to update for each inserted item (slow).  I fixed by pushing range of items instead of one-by-one - UI will be updated once.   Even with this, after a few hundred items, the UI perf will again degrade.  I introduce maxViewItems (default is 100) and one could override via localStorage.

Second, the sort function is slow for large array.  I fixed by ensuring the order in ko.observableArray to have folders before files (as a result, display folders before files).  Within folders and files, the server always returns in alphabetical order (no extra sort needed).

As unrelated fix, I cleanup the wait for Task complexity.  In 4.5, default .NET policy on unobserved faulted task is ignored (unlike 4.0, where the process will crash).