Improve AJAX support

[benjaminpick]

So far, this is implemented in 2.11.0:

• JSON Endpoint
• JS code to access the record of this endpoint
• (Hidden feature) Body class via AJAX

Use this bug report to discuss any improvement ideas.

• Add cookie cache for server response

Roadmap:

1. Next months - Stabilize API (e.g. - I'm not sure if record.get() should support both camelCase and underscore_property), remove Beta flag
2. Sometime in the future - Make it possible that the current shortcodes work automatically also via AJAX. (It will be hard to implement all properties. But I don't want to implement only some and get support requests. That's why it will probably take quite a while.)

[michaelkrieger]

The requirement for jQuery vs raw javascript limits the performance of this to requiring a bulky jquery file. Following the likes of Bootstrap removing jquery's heavy-weight payload.

It should ideally be a Native XMLHttpRequest after prototyping is completed.

[benjaminpick]

Hm, yes that would be better, I might do it at some point - you are welcome to send a pull request if you like ...

[benjaminpick]

The jQuery dependency was removed. I will declare the AJAX API stable soon.

[benjaminpick]

With 4.0 AJAX support (as outlined above) will be complete, see beta branch.