Fix #1254161 [No polish on book's language list](https://bugs.launchpad.net/calibre/+bug/1254161)
Metadata download dialog: Fix current cover not copyable to clipboard
Fixes for various Get Book Polish stores

Merge branch 'master' of https://github.com/t3d/calibre
Ensure that the iso639 translations are used preferentially to translate language names
Merging of HTML files
Implement merging of stylesheets
More robust editor -> preview position syncing
Pre-fill search box with selected text when starting a search
Close search panel when Esc is pressed
Fix for bug #1253922 -- Quickview window is not staying on top of its parent in some *nix systems.
Fix QuickView windows not staying on top on some linux systems

Fixes #1253922 [quickview should be pinned on top of main GUI](https://bugs.launchpad.net/calibre/+bug/1253922)

Merge branch 'master' of https://github.com/cbhaley/calibre
Duplicates dialog, remember window size. Fixes #1254332 [[Enhancement] enlarge the window reporting duplicates after importing new books.](https://bugs.launchpad.net/calibre/+bug/1254332)
Get rid of the workaround for mtpz debug message by compiling libmtp with --disable-mtpz
Make the smart device cache return instances of USBMS.Book instead of Book.Metadata.
Merge branch 'master' of https://github.com/cbhaley/calibre
Fix infinite recursion for unknown translations
Avoid unnecessary traceback when loading plugins that dont have translations for the current UI language
...
Fix plugins that use the polish infrastructure causing circular imports when start tweak book
Fix bug in cloneNode in lxml builder for html5lib parsing