Restore removed qapp.original_font
Better default font when no user font settings detected (happens on linux)
Use the default row height for the book list, rather than resizing to contents, as the Fusion style has a nice default row height

Also allow both increasing and decreasing of the row height
QHeaderView.restoreState() leads to a broken table view when restoring data from different Qt major versions
Remove the notify() debug redirection as it greatly slows down startup and also causes hangs in some not fully understood situations
Start work on a headless QPA plugin to allow Qt to be used without an X server in linux.

Useful for the various command line tools that require
Qt. For example conversion with PDF Output or MOBI output +
rasterization of SVG images. Or ebook-meta with rendering of first page
of EPUB as cover. Or downloading news using a WebKit browser as the
backend.

Makes it unnecessary to use xvfb and will hopefully end the pointless
bug reports from people that try to use calibre command line tools in
environments without X.
Fix building of headless QPA extension on Arch
Rely on PyQt5 being globally importable
Port the new code recently added to master
...
The headless plugin can now locate all system fonts via fontconfig
...
Get rid of install command line tool, since Apple has deprecated the API's it used to obtain root
Use bundles ICU on OS X as well, since we are now no longer generating universal builds
Get rid of the no longer needed libwmf
Add ltdl (required by ImageMagick) to os x build
Remove readline as we no longer depend on it in OS X
Increase minimum required OS X version in the bundle metadata
Add test for netifaces
Add build test for psutil