Make xctool play nice with Find Implicit Dependencies

When xctool builds tests, it generates a throwaway workspace and scheme and then calls `xcodebuild` on that workspace/scheme.

There were 2 problems that prevented implicit dependencies from working -- 

1. The generated scheme needed to set `buildImplicitDependencies = "YES"` if the original scheme said to use implicit dependencies.

2. The generated workspace needed to include all projects in the original workspace given to xctool.  If it didn't, xcodebuild wouldn't have enough information to calculate dependencies.  (Previously, we only included those projects which were mentioned explicitly in the original scheme given to xctool).

This fixes #62 and #16, and xctool will finally play nice with CocoaPods out of the box.