BUG 14753: Consolidated settings proxy creation

Added method to create all settings proxies that haven't yet been
created. This method is now called from
vtkSMParaViewPipelineController and pqPluginSettingsBehavior to ensure
that settings proxies from plugins are registered both when a plugin
is loaded through the plugin manager UI or autoloaded at startup.

Change-Id: I6fe794e80493507d7eb73f084e087d4f22d77afc
Merge topic '14753_PluginSettings' into next

b154c1c4 BUG 14753: Consolidated settings proxy creation