Code base structural refactor, new features and bug fixes

• Major code base file structure refactor. Now all click-related logics are moved to tower_cli/cli/ directory, and exceptions.py as well as compat.py are moved out of utils directory into base directory.
• Categorize help text options for resource action commands (like update) to increase readability.
• Behavior change of workflow schema command. Now schema will both create new nodes and delete existing nodes when needed to make the resulting workflow topology exactly the same as described in schema file.
• Add command job_template callback to enable conducting provisioning callback via Tower CLI.
• Add new format option to just echo id.
• Expand some resource fields, including hipchat rooms for notification template and allow_simultaneous for job templates.
• Lookup related inventory sources with "starts with" logic if its name is not fully qualified.
• Fixed a python 3.5 compatibility issue that causes job monitor traceback.
• Minor typo and help text updates.