fixes #5524

If you are prefer to use spaces instead of tabs - in most cases you
don't want to see tabs anywhere (copy paste issues with other files).

This fixes several workflows:

- Creating new Debug file
- Creating new Tasks file
- Showing global settings (this one is cached, so it shows for the first
  time only right indentation, if you will change it will show old
  indentation till restart)

create workbench using instantiation service and avoid getInstance calls. also pass on the service collection avoid registerSingleton calls

* Support double click on sashes

We had to implement a slight change in the sash drag "hack", by removing the
full cover transparent overlay (that was preventing clicks events from being
fired) and replacing it by a CSS `cursor` rule on the document.body.

The ideal solution for a clean dragging events implementation would be to use
the `Element.setCapture` API that is unfortunately not available in Chrome.

* Center the split editor frontier by double-clicking on it

* Reset the bottom panel size by double-clicking on it

* Implement sash reset on diff editors

* Fix a bug with DOM measurement

The calculus was plain wrong as showed in https://github.com/winjs/winjs/issues/1621
This was probably unotified since this utility function wasn't used in the code base.

* Implement sidebar sash optimal resizing

Fixes #4660

* Abstract `getLargestChildWidth` into a DOM method

This commit also moves the `getOptimalWidth` method from the `Composite` to the
`Viewlet` component. This partially addresses
https://github.com/Microsoft/vscode/pull/4702#issuecomment-207813241

* Calculate the sidebar optimal width correctly in case no folder is open