fixing repetition of paragraphs and grid lines on polymaps images

- Applying fix for grid/thin lines by jasondavies https://github.com/jasondavies/polymaps/commit/a9d879a02afb4ccb54dcbe4534c870ff4dc44efb

- Editing getCurrentColumn function: 
   - to watch for negative heightRemains in previous columns
   - to watch for images in previous columns, if so, check negative height remains in next previous column
   - store the last contentId value so that an undefined contentId is not passed