ZF-6659: Module bootstrap implementation

Description

There is a small hint that module bootstraps are supported in Zend_Application chapter 4.6.3. But important details about how to create a module bootstrap and from which class it should inherit (Zend_Application_Module_Bootstrap) were left. I also expected, that the module bootstraps and environment would be loaded automatically, but it's not mentioned that they would only be loaded when setting e.g. resources.modules[] = in the application ini.

Comments

Documentation added to trunk and 1.9 release branch; will show up on site with 1.9.2 release.