0.5.1: Add operation modes to the scheduler (#13)
* WIP Add scheduler & config * Apply fixes from StyleCI * Create default setting * Clear the sitemap cache if mode is runtime * Register provider, add frequency selection, define defaults * Apply fixes from StyleCI * Add translations for freqency * Cleanup * Apply fixes from StyleCI * Add warning and link to info on setting up the scheduler * Add link to info on scheduler * Tidy * Build JS