improve the legend

by using different letters for each column as suggested by TOBYINK
and also providing a title for each letter
allow tagging columns to not be sorted by table sorter
improve layout for table sorter icons
fix saving of the sort-order to not require a 'table' class and to be able to handle tables with more than 9 columns
apply sorting
tag dashboard columns that shouldn't be sorted, and sort date properly
Merge pull request #1359 from haarg/dashboard-sort

Dashboard sorting
Merge pull request #1358 from szabgab/szabgab/dashboard-legend

improve the dashboard legend