Custom meta field translation UIs

[simonwheatley]

For particular use cases, like Alley's Fieldmanager repeated fields (see slideshow code example), the standard Babble meta field translation UI control will not work as the data is serialised into a single post meta field. In this case users can extend the abstract Babble_Meta_Field class and create their own translation UI control for their own particular use cases.

There are some things we need to join together and fix up to allow this

• [x] Allow HTML on the output (i.e. "to be translated") side of the translation UI control
• [x] Allow the Babble_Meta_Field::update method to alter the value before it is saved
• [ ] Sync untranslated elements of the serialised data (devs could do it themselves, or ignore it, or we might look to see if we can make this easier…)
• [ ] Tests where appropriate

[simonwheatley]

Added a note about syncing untranslated elements of the serialised data; i.e. if the original post is altered, but altered element of the serialised data is not translated (e.g. the image is changed for a slide in a series of slides) and a translation is not triggered (because there's nothing to translate), that image change will not be synced by default. Does that make sense?