Added convenience method for accessing key tasks of a Native Binary

- NativeBinary.tasks returns a DomainObjectSet containing registered tasks for the binary
- NativeBinary.tasks.link and tasks.createStaticLib return these top-level binary tasks
- NativeBinary.tasks.builder returns the link or create task as appropriate
- Added integration test for inserting tasks pre/post linker
Can no longer access default tool chain early in build: assemble sample no longer functions on MinGW or Cygwin.