"Balanced columns" algorithm

This commit include a new algorithm that handle elements height during
the repartition of the items.
The previous algorithm was pretty simple (just balance same amount of
items in each columns), and this can create visual issue if lots of
items have different heights.
I currently have an implementation that can use more than 5000 items, &
with this amount the differences are too big. Checkout an ![commented
example](http://cl.ly/image/1c0N2o181932/Screen%20Shot%202014-03-20%20at
%2021.53.23.png)

Here is a new algorithm that include a small process to retrieve
correct height (by appending them in a additional column
showing/retrieving value/removing ). Using a wrapper to append & remove
from the dom make this very fast. I don’t get any lag with lots of
items on my current board.

Should close #4 (& so close #52 )

A 2nd (simple) commit include fix for latest Chrome (Close #69 & close #40 )

It jshint ok (I've used default grunt) & it should be ok with your coding style. I hope so :)

It not _really_ better on your example (in the repo) since the images doesn't have the appropriate height during loading, but in my case it give something really great (fyi I use https://github.com/suitcss/flex-embed/ to prepare my css to avoid issue like that, very nice for rwd).

This algorithm part should be easily skipped if wrapper in a conditional part (that can be enabled with an option).