Open test of map tile improvements

@pleary – i noticed one minor thing. when you click on a grid cell, it opens a pop-up for an observation (the latest one in that cell?). that’s fine, but i think the area that you click on to trigger the pop-up is actually offset slightly down a few pixels vs the cell. (i noticed this behavior because i had a situation where there was a cell just above another cell, and clicking on either cell seemed to trigger the same pop-up corresponding to the upper cell. i had to click on the bottom half of the bottom cell or a few pixels below it to trigger its pop-up.)

UPDATE: i mocked it up with UTFGrid in green on top of the geotile grid, and it looks like a cell from the geotile grid actually gets represented as 5 one-fourth size cells arranged in a plus sign, instead of 4 one-fourth size cells arranged in a square to match the original cell. i think that’s why i can click below the cell and trigger an action, and i can also click to the right of the cell an also trigger an action.

i think there’s always been a bit of a mismatch between the markers and the UTFGrid representation, but it’s particularly noticeable in the new grid because it’s a grid without overlapping markers.