refactor routes,

use json encoding for route body parameters,
implement modify user/group/pool operations,
simplify schema by using comon lib struct tags and RequireAll and AtLeastOne helper functions,
properly implement locadb as Backend interface

app/common/schema.go

@@ -1,21 +1,7 @@
 package app
 
 type Login struct { // login body struct
-	UsernameRaw string `form:"username" binding:"required"`
+	UsernameRaw string `json:"username" binding:"required"`
 	Username    Username
-	Password    string `form:"password" binding:"required"`
-}
-
-type UserFormRequired struct { // add user body struct
-	CN       string `form:"cn" binding:"required"`
-	SN       string `form:"sn" binding:"required"`
-	Mail     string `form:"mail" binding:"required"`
-	Password string `form:"password" binding:"required"`
-}
-
-type UserFormOptional struct { // modify user body struct
-	CN       string `form:"cn"`
-	SN       string `form:"sn"`
-	Mail     string `form:"mail"`
-	Password string `form:"password"`
+	Password    string `json:"password" binding:"required"`
 }