Replace basic auth with cookie authentication (#440)

* Add logout functionality and button
* Make session age configurable

vendor/github.com/gorilla/sessions/cookie.go

@@ -0,0 +1,19 @@
+// +build !go1.11
+
+package sessions
+
+import "net/http"
+
+// newCookieFromOptions returns an http.Cookie with the options set.
+func newCookieFromOptions(name, value string, options *Options) *http.Cookie {
+	return &http.Cookie{
+		Name:     name,
+		Value:    value,
+		Path:     options.Path,
+		Domain:   options.Domain,
+		MaxAge:   options.MaxAge,
+		Secure:   options.Secure,
+		HttpOnly: options.HttpOnly,
+	}
+
+}