Style parameter blacklist

Style files are no longer allowed to configure settings unrelated to the style to prevent unexpected consequences. These parameters include the following:

'interactive', 'backend', 'backend.qt4', 'webagg.port', 'webagg.port_retries', 'webagg.open_in_browser', 'backend_fallback', 'toolbar', 'timezone', 'datapath', 'figure.max_open_warning', 'savefig.directory', tk.window_focus', 'docstring.hardcopy'