Added toastr.less - a LESS port of toastr.css

Hi Guys,

I've recently started making use of toastr (good work by the way!).

In most of my own projects I've started switching over from using direct CSS to using LESS.  If you're not aware of it, LESS is a very simple CSS pre-processor that I've found makes for more manageable code (and I find out sooner if I've made a mistake in my LESS than than I would with my CSS :+1: ).  

For that reason, I created myself toastr.less based on toastr.css which is simply a LESS version of what existed before.  This LESS file can be used to generate both toastr.css and toastr.min.css.  

It's useful to me and on the off chance it's useful to you I thought I'd send you the fork - don't feel obliged to to use this if LESS isn't your bag.

All the best - and thanks for toastr!

John