Node.js table unpin

[texodus]

Fixes #841

• Removes the empty view() which kept hosted table alive. <perspective-viewer> no longer deletes it's table when it is itself deleted, so this is not default deleted (though it can still be explicitly deleted remotely - probably something to change later).
• Adds on_delete callbacks for both, unhosting objects when they are deleted.
• Adds eject_table() and eject_view() methods.

[andyferris]

Awesome, thanks @texodus!