Export when as an ambient external declaration
Support ko.dependencyDetection

Add ko.dependencyDetection alias and extend KnockoutComputedContext to
have all the other methods on it.
Merge branch 'knockout_dependencyDetection' of https://github.com/Nemo157/DefinitelyTyped
Merge branch 'when-as-ambient-external-declaration' of https://github.com/Nemo157/DefinitelyTyped