feat(typeahead): adding/removing class when source is promise

[skytracer]

I think it would be nice to set a class to mark the beginning and the end of the async source pull
I am using this to show a spinner at the right end of the input.
This is my code

             var getMatchesAsync = function(inputValue) {

                    var locals = {$viewValue: inputValue};
                    element.addClass('bs-searching');

                    $q.when(parserResult.source(scope, locals)).then(function(matches) {

                        //it might happen that several async queries were in progress if a user were typing fast
                        //but we are interested only in responses that correspond to the current view value
                        if (inputValue === modelCtrl.$viewValue) {
                            if (matches.length > 0) {

                                scope.activeIdx = 0;
                                scope.matches.length = 0;

                                //transform labels
                                for (var i = 0; i < matches.length; i++) {
                                    locals[parserResult.itemName] = matches[i];
                                    scope.matches.push({
                                        label: parserResult.viewMapper(scope, locals),
                                        model: matches[i]
                                    });
                                }

                                scope.query = inputValue;
                                element.removeClass('bs-searching');

                            } else {
                                resetMatches();
                            }
                        }
                    }, resetMatches);
                };

[pkozlowski-opensource]

@skytracer thnx for your input and inspiration but I don't think we should be adding classes like this. Doing so would mean that we are doing DOM manipulation on every keystroke and also we would be hard-coding a CSS class.

But the use-case you've got is very valid so I would propose to solve it slightly differently. The typeahead directive could expose the loading binding expression (would have to be a settable property). Then you could use it with ng-class to style an input, ex:

<input ng-model="mymodel" typeahead="..." typeahead-loading="isLoading" ng-class="{myLoadingStyle: isLoading}">

WDYT?

[pkozlowski-opensource]

BTW: it is somehow linked to #192 although here we should really focus on exposing a binding variable only. This would actually allow people to implement #192 "by hand". I still think we should implement #192 to have a default loading behavior.

[pkozlowski-opensource]

@skytracer I've implemented an alternative, model-oriented approach in b58c9c8, as described above. Let me know what do you think.

[skytracer]

@pkozlowski-opensource I think your approach opens more use-cases and I am happy with it
Thanks