keyPressEvent/etc no longer work with qwebengineview, so we need to
install an event filter to catch things like ctrl+c. drag & drop
doesn't seem to be supported until 5.7
- a few issues to work out still, and editor changes not done yet
- for communication between webengine and python code, we set window
.location to 'http://anki/<something>' - the leading http is
necessary for qt to call the link handler, which was introduced
in qt5.5
- the designer files now use a promoted qobject to create instances
of AnkiWebView
- we use the css zoom property to alter webengine font size based on
system dpi
- prefs and addons folder stored in new location (at least for now)
the canFocus/canCopy separate variables was silly, as we ended up
with text that could be copied from the context menu but not with
a shortcut key. also we default to allowing focus now, since that's
the more sensible default. fixes copy issues with card info dialog and
some addons
