Fix next activity form ajax behaviour

If you made an error and submit again, it wasn't ajaxified anymore
That was due to the fact the options passed to the form creation the
first time were not used in the ajax view, here we fix it.
Put it in alphabetical order and change pyramid_deform requirement
Fix buttons in nextactivity form
Send the form again after programming a new activity
Provide a _get_form method on BaseFormView

it allows for example to return the form again in a submit_success
method
Fix missing return
Fix icon name