Replace easyautocomplete with Awesomeplete

[tfrancart]

We are stuck with easyautocomplete because it does not provide a handle function to build the autocomplete list : either we pass it the full list of labels, or a URL, and it manages to call it. But since we now want to call multiple URLs to build the list, we need our custom function.
Plus easyautocomplete is not maintained anymore, and the website is broken.
Better move to Awesomeplete : https://projects.verou.me/awesomplete/, which does not depend on JQuery (and has much more Github stars BTW)

See https://projects.verou.me/awesomplete/#advanced-examples the example "Custom list example (based on user input)" : this is what we need to do.