Added new configuration parameter activeHeaderRowIndex, which allows to
set header row, that determines column count and which listens to click
events; defaults to last header row otherwise; slight code cleanup: when
the entire table body has been changed (for example by setting
innerHTML), an sorTable.initSort() rereads row data and allows a
subsequent reSort()

Change-Id: Ia8554c141591d46c077beb1455e29f90784c4070