What (a) is the total cost of legal expenses incurred by the Financial and Fiscal Commission (FFC) (i) in the 2017-18 financial year and (ii) since 1 April 2018, (b) percentage of the total expenses incurred by the FCC is constituted of legal expenses in each case and (c)(i) is the total number of cases, (ii) are the details of the legal matters covered in each case and (iii) is the total cost incurred for each case?