Spinner changes

We get rid of the spinner in the toolbar, since load information is
already given by the floating status indicator inside the WebView.

The only remaining spinner is the one in the tabs, which has been
ported to use GtkSpinner.

Get rid of EphySpinner.

Fixes:
https://bugzilla.gnome.org/show_bug.cgi?id=524809 (again)
https://bugzilla.gnome.org/show_bug.cgi?id=598442