[#83716236] Fix aspect ratio when scaling images for 'match' levels, and give boxes uniform borders.
Adjusting colors to match the official color guide, applying a darker dotted outline to droppable areas (communicates the swap option better) and added a hover color and cursor change to moveable tiles.
Vertical-center images on match tiles.
Compatability pass: Now works in IE9, Safari 4.
Merge pull request #851 from code-dot-org/83716236_match_blocks_proportional_scaling

#83716236: Match blocks proportional scaling of images