allow users to hide/show email address (closes gogs#3358)

* add ShowEmail bool to User model
* add show/hide email checkbox on user profile settings form
* add show/hide email checkbox on admin edit user form
* add ShowEmail to user profile settings post handler
* add ShowEmail to admin edit user post handler
* show/hide emails on user profile and users directory per User.ShowEmail
* add en/US translation for 'show_email'

Author: bill-auger

modules/auth/admin.go

@@ -28,6 +28,7 @@ type AdminEditUserForm struct {
 	LoginName        string
 	FullName         string `binding:"MaxSize(100)"`
 	Email            string `binding:"Required;Email;MaxSize(254)"`
+	ShowEmail        bool
 	Password         string `binding:"MaxSize(255)"`
 	Website          string `binding:"MaxSize(50)"`
 	Location         string `binding:"MaxSize(50)"`

modules/auth/user_form.go

@@ -91,7 +91,7 @@ type UpdateProfileForm struct {
 	Name      string `binding:"OmitEmpty;MaxSize(35)"`
 	FullName  string `binding:"MaxSize(100)"`
 	Email     string `binding:"Required;Email;MaxSize(254)"`
-	ShowEmail bool   `form:"showemail"`
+	ShowEmail bool
 	Website   string `binding:"Url;MaxSize(100)"`
 	Location  string `binding:"MaxSize(50)"`
 	Gravatar  string `binding:"OmitEmpty;Email;MaxSize(254)"`