Show namespaces in package explorer for composer managed build path folders

[gossi]

This is a feature PDT once had after the introduction of PHP5.3. They showed namespaces instead of sourcefolders (unfortunately pdt didn't show anything else in the project, which was the biggest mistake). It tried to simulate the look and feel of JDT but could not completely make it work, because of missing metadata. Now that composer and the composer plugin can offer this metadata through the namespace resolver, all build path folders, that composer manages can be displayed showing namespaces, instead of a folder structure.

Should become available through a switch in PHP Explorer toolbar.