Make Sandcastle autocomplete work without combine step.

Sandcastle had an uneeded dependancy on `Build/CesiumUnminified/Cesium.js` (generated during the combine step) since the `Source/Cesium.js` file could provide the same functionality (and is created during the build step).

This means that for a fully functionaly sandcastle you only need to run `build` and `generateDocumentation` which is way faster than `combine and generateDocumentation`.