Support legacy code inside bundles.
Code located in Resources/ezpublish-legacy is loaded as a legacy extension named after the bundle.
- make it easier/automatic (compile time ?) to map a fieldtype to the null fieldtype. Use-case: soft migrate a legacy fieldtype extension to a bundle, and make it not break the system by mapping it to a bundle.
See specifications for more details: https://gist.github.com/bdunogier/8556028 (comments on the gist welcome)