Ignore paddings and borders of column headers and cells when their box-sizing CSS property is set to border-box
Set a correct width for the column header placeholder
Add support for vendor prefixes
performance improvement

Conflicts:
	slick.grid.js
remove numberOfRows private member because it only used in UpdateRowCount.
remove not used variable
Fix #738 - Use an object instead of an array to hold groups by value.
Merge pull request #699 from Morhaus/box-sizing

Support the "box-sizing: border-box;" css rule for column headers
Merge pull request #725 from kzhdev/performance

Performance Improvement