Change thumbnail default size and resize algorithm (#336)

* Change thumbnail resize algorithm and add size parameter

* Height -> Width

* Change default size from 100px to 200px

* Height -> width

pkg/manager/manager.go

@@ -28,6 +28,7 @@ var once sync.Once
 type flagStruct struct {
 	configFilePath string
 }
+
 var flags = flagStruct{}
 
 func GetInstance() *singleton {