Replacing t variable to _this

We are using t variable to allow passing the this context to inner functions. Using t as the name considered as coding smell and it is best to be replaced to more meaningful name like _this.
Adding changes in error reporting to support Lint check and IE8

Adding global window, console to jslint global lists in order to allow jslint grunt test to pass. Test was failing since the jslint requires global variable declaration of every global variable being used. In order to not breaking old browsers (IE8), I've also added test of window.console.
Adding 1.5X support to srcset

srcset was being generated to 1,2,3,4,5 zooms. Photon and other image services also supports 1.5X zoom images so srcset of 1.5X is also being generated.