(a) How many arrests were made by the Directorate of Priority Crime Investigation (i) in the (aa) 2010-11, (bb) 2011-12, (cc) 2012-13, (dd) 2013-14 and (ee) 2014-15 financial years and (ii) since 1 April 2015 and (b) what total number of the specified arrests resulted in secured convictions?