Fixing #42: Authentication Screens UI: Input Text Field

This is the widget used to create the input text field used in the authentication screens. It takes :

1. [placeholder] as the placeholder text.
2. [inputType] as the type of input whether mail or password,
3. [controller] as the controller for the text field
4. [onTap] as the function that will be called when the text field is tapped
5. [onSubmitted] as the function that will be called when the text field is submitted
6. [label] as the label text of the text field
7. [isRequired] as a boolean that determines whether the text field is required or not
8. [errorText] as the error text that will be displayed if there's an error in the text that user entered.