Uses a form backstage (i.e. the form is never visible to the user) to actually send the updated values to the server.

This fixes the "IPE form won't go away after saving" bug.

What does work:
- click on a field formatter that has the 'form' IPE type
- an inline form will appear
- change the values in this form
- click "save"
- the rendered field will be updated! (But you cannot edit it again … yet!)

Distinguish between a $field and an $editable. This is necessary to accomodate different types of IPE.

- $field: corresponds to the field wrapper.
- $editable: corresponds to the editable for this field, which is the field wrapper for .ipe-type-form, but it's something *within* the field wrapper for .ipe-type-direct.

Add the proper wrapping + metadata to the node author and authoring date so that we can do IPE on it.

Add identifiers for each field (as IPE-prefixed data- attributes); this allows us to easily correlate data/requests to specific fields on the page.

Leverage the fape (Field API Pane Editor) module to generate forms for each field. (This patch adds the back-end only.)

Decide on the type of IPE based on 1) the field formatter, 2) the field's cardinality. Previously: based on the entity's view mode.

Simplify some often-used class names: s/.ipe-editable-allowed/.ipe-allowed/, s/.ipe-editable-candidate/.ipe-candidate/

Editable fields are now only marked as editable if the user has permission to do so. Plus: proper labels.

Editable entities (well, currently just nodes) are now only marked as editable if the user has permission to do so. Plus: proper labels, actual edit links.

Track if the content of the currently being edited field has changed; only allow editing to be ended when it has not changed.

Editable entities. Distinction between highlighting an editable and editing an editable. All behaviors work correctly.

View/edit mode toggle. Toggling works. Editable fields are highlighted. Operations toolbar works. First version that actually shows something meaningful :)

Comments consistent with core; rename our #pre_render overrides for clarity and to prevent a naming clash.