Add error messages for autocomplete - Closes #823

[ginacontrino]

What's the Problem?
We make an unnecessary request every 10 second just to check if the client is online or not.
#823

What did you do?

• added an extra check and added error message
• added one translation

How can I test this?

• go to "Vote"
• check for both "Add vote to" and "Remove vote from" that :
  • the search is still working (showing results)
  • when you search for something that doesn't exist, the autocomplete should be blank and the
    error message "No matches" appears

It should look like this:

[slaweet]

Well done @ginacontrino