Collection of little things to fix

[garado]

• Allow parallel downloads
• When downloading new individual GTFS feeds: remain on GTFS browse screen to allow multiple individual selections, instead of going back to the downloads screen immediately
• Redesign GTFS manager screen
• Automatic GTFS downloads when searching a new area?
• Fix Kosovo country code (XK)
• Check for updated GTFS feeds
• Navigation screen always shows minutes when other time units would be more appropriate (e.g. "in 912 minutes"