Grouped some API controllers by functionality

api/system.go

@@ -0,0 +1,15 @@
+package api
+
+import "github.com/deluan/gosonic/api/responses"
+
+type SystemController struct{ BaseAPIController }
+
+func (c *SystemController) Ping() {
+	c.SendResponse(c.NewEmpty())
+}
+
+func (c *SystemController) GetLicense() {
+	response := c.NewEmpty()
+	response.License = &responses.License{Valid: true}
+	c.SendResponse(response)
+}