Move towards better integration of text form field and TextEditingController

[piotruela]

Currently, the 'standard' way of working with form fields that are text fields is to wrap Text(Form)Field with FieldBuilder that provides an instance of TextFieldCubit and to set onChanged param of widget to fieldCubit.getValueSetter() so that each time onChanged is called the value is set in the TextFieldCubit state. We should provide a better integration with TextEditingController.

• Changes in the TextEditingController.value should be passed to field cubit state,
• Changes applied to the field cubit state (value), should be streamlined to text controller.

Related issue: #21