CSettingsManager: SettingsHandlers is std::vector now, because we need
to preserve the order the handlers where registered. Duplicates are
avoided in CSettingsManager::RegisterSettingsHandler. CSettings: Changed
the order ISettingsHandlers are registered.
Merge pull request #3394 from groth-its/fix-pathsubstitution-rss

settings: load CAdvancedSettings first to fix CRssManager