beginning implementation of MixtapesViewController
filtering out of albums complete
added designated initializer of DHDataSource that accepts cell height argument
removed initWithItems:cellHeight:cellIdentifier:configureCellBlock: from DHArrayDataSource as tableView:heightForRowAtIndexPath: is a delegate method
fixed mixtape tableView cell height issue
added constant variable for cell height in TracksTableViewController
added constant global accessors for mixtapeCoverHeight and mixtapeCoverParallaxSpeed to MixtapeCell.h and definition in MixtapeCell.m