fix(tabs) - fixed dependency and empty tab content logic

- Resolved dependency upon `material.services.registry`
- show tab content if any tab is non-empty
- toggle tab content visibility when tabs are added or removed.
- ignore tab content with comments only.
demo(tab) - updated to show logo in tab header
fix(ink) - resolved missing service `$$rAF` argument
feat(tab) - clarify function name for usability
fix(ink) - improved logic for `effectAllowed()`

- checks if scope has flags to allow ink ripples
- check if parent is `disabled` and prevents ink ripples
- no longer removes the mouseDown listener; support dynamic changes to `disable` flag.