What number of social worker students were registered for (a) 1st year and (b) 4th year of study at all respective universities in (i) 2005, (ii) 2006, (iii) 2007, (iv) 2008, (v) 2009, (vi) 2010, (vii) 2011, (viii) 2012, (ix) 2013, (x) 2014 and (xi) 2015?