Setting `element.style.display` to `null` in IE11 has no effect.
So if the suggest widget was hidden for some reason, and then
shown again, it just stayed hidden.

This issue also prevented the "No suggestions" message from displaying.

Fixes: https://github.com/Microsoft/monaco-editor/issues/96

https://github.com/Microsoft/TypeScript/issues/10220

Fixes Microsoft/monaco-editor#2: Fix scrollbars, context menus, mouse operations and content widgets layouting when editor is inside a position:fixed container

* 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