Implement column sums in tablefooter

[alexkleinwaechter]

Hi there,
first of all thank you for the great work done in this Boilerplate. I try to enhance the entitytable to get the sum of a specific decimal field in to the tablefooter. Due to the generic aproach I just don't get it running.

Has anyone here tried it and was luckier than me?

Best!
Alex from Berlin