The RJS field marks it as required, and user can't submit anymore.
Instead, use an external validator to only require the field when the user submit

In reality, it should be done by internally only using changeState, but that's another story

Stop using the update action as the default action.

It seems the commit reimplement a kind of adhoc changeState

- Allow to continue to edit a form while saving is on going
- Reset fields on form view update (like by clicking on the active tab from the panel)
- Fix rendering an input like gadget with the same value as rendered before causes the
  gadget to be not updated even if the field has been manually edited.

/bug #20190204-39AF19
https://nexedijs.erp5.net/#/bug_module/20190204-39AF19

/reviewed-on nexedi/erp5!861

This reverts commit b3ff3ec4.

Fetch usage can be bypassed to do not use service worker when not needed.

As appcache has been dropped on Firefox, this change will improve the speed on Firefox.

No change is expected on Chrome/Safari.