What is the total number of firearms that (a) are currently registered in the Central Firearm Register (CFR) and (b) were registered on the CFR as at (i) 31 December 1994, (ii) 31 December 1996, (iii) 31 December 1998, (iv) 31 December 2000, (v) 31 December 2002, (vi) 31 December 2004 and (vii) 31 December 2006?