Adding ability to define custom screen sizes

added itemsCustom where you can set various dimensions of the browser
width as example:

itemsCustom : [
  [0, 2],
  [450, 4],
  [600, 7],
  [700, 9],
  [1000, 10],
  [1200, 12],
  [1400, 13],
  [1600, 15]
],
Merge branch 'pr/104' into v1.31
v1.31
Merge branch 'v1.31'
Changelog Update