Review/fix signup.go page

[devzeeh]

Fix the signup.go for correctness, fields, password length, Database errors.

• Steps to reproduce
• User not found or DB error: Error 1146 (42S02): Table 'paycard_playground.persons' doesn't exist

// Check if fields is empty
	if user.Username == "" || user.CardNumber == "" || user.Password == "" {
		h.Tpl.ExecuteTemplate(w, "signup.html", ErrorMessage{Error: "Please check all fields."})
		return
	} 
This should be removed in line 68 - 72

// Get form values using User struct
	user := User{
		Usertype:   "Regular",
		Username:   r.PostFormValue("first_name"),
		Fullname:   r.PostFormValue("first_name") + " " + r.PostFormValue("last_name"),
		CardNumber: r.PostFormValue("card_number"),
		Password:   r.PostFormValue("password"),
		Email:      r.PostFormValue("email"),
		Phone:      r.PostFormValue("contact_number"),
	}
Remove unnecessary variable here that not included in frontend side (HTML)

• fix overall signup page for clarity.