XCOMMONS-383: First level of upgrade plan tree contains all extensions and not only the non-dependencies extensions on a subwiki
(cherry picked from commit 68fc6eeafc6940bb83056d3c55cd9753800d454b)

Conflicts:
	xwiki-commons-core/xwiki-commons-extension/xwiki-commons-extension-api/src/test/java/org/xwiki/extension/repository/installed/DefaultInstalledExtensionTest.java
	xwiki-commons-core/xwiki-commons-extension/xwiki-commons-extension-api/src/test/java/org/xwiki/extension/repository/local/DefaultExtensionSerializerTest.java