Remove get_task_name function

Task names should be obvious and consistent to users. get_task_name confounds user's attempts to configure tasks by hiding the name of the task (as seen by runner).
Sort root task graph nodes by name

Users expect non-configured tasks to run in sorted order (like init scripts).
Add test for tasks sorted by name.
Revert "Remove get_task_name function"

This reverts commit 591a9cc00e48362d24b533b841e9e779e4a38b0d.
Merge pull request #18 from mrrrgn/sorted-tasks

Sorted tasks