Document better how form submissions work

[binarykitchen]

Videomail-Client has a submission hook. It overrides the default form submission, submits the Videomail first to the Videomail server and only then resumes with the real form submission. Had to be like that. Hence the Videomail-Client needs to know the form tag and the submit button. For that there are options, i.E.

          selectors: {
            submitButtonSelector: 'body input[value="Submit"]',
            formId: 'someForm'
          }

See example at https://github.com/binarykitchen/videomail-client/blob/develop/examples/contact_form.html#L55\

For some it can be irritating why the form gets submitted without any vidoemail information because the onSubmitted event is called too late. Exactly because of this.

[binarykitchen]

done, good improvement