Refactor event handlers for voting news and comments.
Add missing event handlers for voting the main comment in the comment page.
Remove 'apisecret' from the parameters for the voting event handlers.

The apisecret variable lives in the global scope, so there is no actual need to
pass it around as an argument.
Implement a more generalized event handler for voting news and comments.
Add an optional callback parameter that is called after voting an item.
Generalize the procedure to attach voting handlers to the selected elements.
Merge remote-tracking branch 'nrk/refactor_voting_handlers2'