fshttp: Add cookie support with cmdline switch --use-cookies

Cookies are handled by cookiejar in memory with fshttp module through
the entire session.

One useful scenario is, with HTTP storage system where index server
adds authentication cookie while redirecting to CDN for actual files.

Also, it can be helpful to reuse fshttp in other storage systems
requiring cookie.

fs/config.go

@@ -85,6 +85,7 @@ type ConfigInfo struct {
 	MaxBacklog            int
 	StatsOneLine          bool
 	Progress              bool
+	Cookie                bool
 }
 
 // NewConfig creates a new config with everything set to the default