IDE-1557 refactored codes about descriptor helpers

- move classes of descriptors to com.liferay.ide.project.core.descriptor
- make class LiferayDescriptorHelper abstract
- new way to invoke descriptors' operations
- rename LiferayProjectCore class to ProjectCore
IDE-1557 Source formatting
Test fixes
Refactored ProjectUIPlugin ==> ProjectUI
Included eclipse-wtp-xml-search core feature into updatesite
IDE-1607 added support for service wrappers