#014273: Deprecate eZModuleManager::availableModules() in favor of the ModuleList[] setting

Instead of searching files on the file system, it should rely on the ModuleList[] setting.

Advantages:
- speed improvement
- one single way to retrieve the available modules

Extensions that currently do not have this setting but should have, might cause issues with the URL alias system, so at a certain point in time they'll have to be corrected anyway.

Operating System:
PHP Version: (please be specific, like '4.4.3' or '5.1.5')
Database and version:
Browser (and version):