[MM-13840] Change eMail as a post-verification action (#10253)

* Change eMail as a post-verification action

* Fix broken test

* comment for special behavior, tests

* govet

* Check for already existent eMails when require email verification is turned on before accepting update

app/import_functions.go

@@ -477,7 +477,7 @@ func (a *App) ImportUser(data *UserImportData, dryRun bool) *model.AppError {
 		}
 		if emailVerified {
 			if hasUserEmailVerifiedChanged {
-				if err := a.VerifyUserEmail(user.Id); err != nil {
+				if err := a.VerifyUserEmail(user.Id, user.Email); err != nil {
 					return err
 				}
 			}