Don't show ephy-about: in the UI

https://bugzilla.gnome.org/show_bug.cgi?id=720876
Don't show null in page title for about:plugins

If for some reason an about: page doesn't load the next startup
will show one of the error screens. Those screens assume they
can get a hostname for the URL. There is no hostname for about:
schemes. So, in that case just display the entire URL.

https://bugzilla.gnome.org/show_bug.cgi?id=720876
Always use a favicon in the drag surface

https://bugzilla.gnome.org/show_bug.cgi?id=720876
Center the favicon vertically on the drag surface

https://bugzilla.gnome.org/show_bug.cgi?id=720876
Add more padding around the drag surface

https://bugzilla.gnome.org/show_bug.cgi?id=720876
Increase the row padding in the completion menu

https://bugzilla.gnome.org/show_bug.cgi?id=720876
Match spacing in current Adwaita

https://bugzilla.gnome.org/show_bug.cgi?id=720876
Use a smaller text size for the url line in the completion menu

https://bugzilla.gnome.org/show_bug.cgi?id=720876