fix for options.target is ignored after first clear() or notify() issue

Hi, 
There is a bug in that the options.target changes are ignored after $container was once created. I.e. it's impossible to move the toastr $container to other parent with a next notify() call. 
Same thing is when there was a call of toastr.clear() before toastr.notify(), it would be impossible to specify target with notify call options. 

A way to reproduce : 
1. http://jsfiddle.net/igoryan/zgs9F/2/
2. Click "Show on div2". Container stays the same, where it should have been moved to ".div2".

Please consider the proposed fix.