[WIP] Add X-editable (edit in place) support in lists

Related to #1440

This PR adds XEditable (edit in place) support in lists. Validation errors are handled.

It currently works with the following (scalar) types : 
- text
- textarea
- email
- string
- smallint
- bigint
- integer
- decimal
- currency
- percent
- url

More complex types (date, choices...) may require more work.

![capture3](https://f.cloud.github.com/assets/663607/1786674/1b1f5dd0-68f9-11e3-8693-01863312d43a.PNG)
![capture](https://f.cloud.github.com/assets/663607/1786715/c6054b92-68f9-11e3-9336-10d20215e26f.PNG)
![capture2](https://f.cloud.github.com/assets/663607/1786661/fb248d2a-68f8-11e3-9de4-f67feb5477bc.PNG)