STOCK PURCHASE AGREEMENT by and among Epiq Systems, Inc. (solely for purposes of Sections 4.1, 4.2, 4.3, 4.5, 4.6, 4.7, 4.8, 4.9, 4.10, 7.3(a), 10.2, 10.3 and 11.17) and Epiq Systems Holding Company and Encore Intermediate Holdco, Inc. and ELS...