* move email unsubscription page outside of API and make it HTML
* make separate HTML template for SendErrorHTML
* fix error template name
* add test for SendErrorHTML, introduce MustExecute function
* fix content check in test of TestSendErrorHTML
* fix logging test to be more generic and not depend on line numbers
- Adds common function to get error message from the http response
- Adds error message for the voting displayed under the voting buttons
- Adds restoring of voting data after voting request failed
fixed re-writing error message when user tries to vote for the same comment