Fix crash with providers initialization

 * Stop on initialization error
 * Prevent uninitialized worker from being added to the pool
Split workers code file per worker type
Fix graphite connector
Fix typo in worker_provider.go filename
Fix redirection warning with UI API calls
Remove unneeded UI element in scale management
Fix human readable formatting with negative values
Fix `Move Up` action in graphs management
Fix various Administration Panel issues

 * Fix stuck form issue after metric edition in graph management
 * Fix incorrect origin selection when editing group
Honor plot query scales in graphite connector
Add duration to range conversion in `utils`
Update request structure in `facette` connector
Facette connector returns upstream plots results
Remove debug output in facette connector
Add context to error messages in facette connector