#6 misc visual improvement

[Matt Stucky]

column headers are links with sort up/down right now. improve to look slightly different. also, when a column is sorted change the header or the background of the column (without adding extra width) to indicate the current sort. maybe put a down-arrow graphic as the background for the colum header cell, for example.

also, the links in the main data table that allow 'filter-to' capability, again, those should look clickable but visually indicate (better) what it is
they do.

third, add tooltips on mouseover.