Improved: Refactor the startup API to completely remove the startup loaders collection

This commit refactors the startup bootstrapping logic to remove any references to the
StartupLoader API and any related files. This is due to the fact that any loaders
including the old POS is completely removed from the system. Thus this improvement
simplifies the startup logic and makes it easier to maintain.

Thank you: Mathieu Lirzin for the patch, careful review and patience


git-svn-id: https://svn.apache.org/repos/asf/ofbiz/ofbiz-framework/trunk@1852847 13f79535-47bb-0310-9956-ffa450edef68