ullFlow externals

ullFlow externals are used for complex fields like file upload.

How it works:

In the edit action:

A ullMetaWidgetUpload handles the display of the edit mode. The real value of the column is in a hidden field.

Then there are fields ull_flow_action, external, external_field and a Button "Manage files"

A click on the button submits the whole edit form to the update action

The update action checks for a request param "external". If it finds one it tries to execute the corresponding ullFlowExternalUpload class, gets a module and a action from it, and redirects to it.

The External itself is now a normal symfony action + template.