Begin refactor to better encapsulate configuration

This also updates the example_config.json which did not previously work.
Config.Config is now composed of embedded structs of other configs that
can later be used to clearly have a separation of concerns.

tracker/storage.go

@@ -35,7 +35,7 @@ type Storage struct {
 func NewStorage(cfg *config.Config) *Storage {
 	s := &Storage{
 		users:   make(map[string]*models.User),
-		shards:  make([]Torrents, cfg.ShardConfig.TorrentMapShards),
+		shards:  make([]Torrents, cfg.TorrentMapShards),
 		clients: make(map[string]bool),
 	}
 	for i := range s.shards {

tracker/tracker.go

@@ -27,7 +27,7 @@ type Tracker struct {
 // New creates a new Tracker, and opens any necessary connections.
 // Maintenance routines are automatically spawned in the background.
 func New(cfg *config.Config) (*Tracker, error) {
-	bc, err := backend.Open(&cfg.Backend)
+	bc, err := backend.Open(&cfg.DriverConfig)
 	if err != nil {
 		return nil, err
 	}