Changed minimum accepted card limit to 0

User scenario: We had a card lane named "Blocked" which should not have any card ideally. This change is to cater that need.
updated coloring logic when cardLimit is 0

When there are no cards in a card lane with card limit of 0, the lane should not have 'at-limit' class attached to it.
Merge pull request #3 from subinvarghesein/master

Changed minimum accepted card limit to 0