Change the way progressbars and legends are rendered

1) Use <table> instead of fancily positioned divs
2) Use relative widths, use CSS styles for coloring instead of images; this makes the size of the progressbar adjustable via CSS
3) Remove legend block; instead, show legend in the tooltip
4) Make the top progressbar of the translation project overview page of 100% width

Note: not sure if just deleting the obsolete images is enough; it seems they are still there in the sprite PNG/CSS.