Maven: moving methods from class into instance.

This will allow us to start doing dependency injection for behavior that
can be driven from CLI options, like better debug/log messages.
Gradle: moving methods from class into instance.

This will allow us to start doing dependency injection for behavior that
can be driven from CLI options, like better debug/log messages.
CocoaPods: moving methods from class into instance.

This will allow us to start doing dependency injection for behavior that
can be driven from CLI options, like better debug/log messages.
Refactoring DependencyManager

now that we're using instances of all the package manager classes.