fix(olHelper): use ol.format.GeoJson.readFeatures
fix(olHelper): use ol.format.GeoJson.readFeatures

Fixed bug where GeoJSON sources did not parse WFS features.
oSource.readFeatures is an undefined function, so used
ol.format.GeoJson.readFeatures instead.

ageblade/angular-openlayers-directive,mikostn/angular-openlayers-directive,claycephas/angular-openlayers-directive,chambleton/angular-openlayers-directive,gaf-ag/angular-openlayers-directive,polesapart/angular-openlayers-directive,StevenHeinrich/angular-openlayers-directive,milafrerichs/angular-openlayers-directive,tombatossals/angular-openlayers-directive,birdlifedk/angular-openlayers-directive,mikostn/angular-openlayers-directive,TeChn4K/angular-openlayers-directive