userpage: initial page

login, lang, and theme work. Currently only makes a request to a
hello-world type endpoint to verify auth works. Accessible at
/my/account.

api-userpage.go

@@ -0,0 +1,7 @@
+package main
+
+import "github.com/gin-gonic/gin"
+
+func (app *appContext) HelloWorld(gc *gin.Context) {
+	gc.JSON(200, stringResponse{"It worked!", "none"})
+}