testing another double page implementation

https://github.com/etabard/Reader/commit/58002e6121b5109a5c3d400cdf2a144
23980cb1b
adapting etabard's double page implementation

ReaderViewController
adapting etabard's double page implementation

ReaderContentView
fixed increment/decrement page overflows
fixed doubletap to zoom
fixed overflow in page number on single last pages
removed legacy code
removed some minor differences to etabard's code
page preview & shadow fix
Merge branch 'double-page-by-etabard'