[misc] Bulletproofing.

(cherry picked from commit 882dfc9655d5cf1918763104ba03fa954cfb2c58)
XWIKI-10186: Duplicated root namespace extension in DW "Extensions" step
* Fix left-over usage of upgrade mode.

(cherry picked from commit 55e79a0360a737b63a5da99635edd8e568728d0a)
XWIKI-10210: Extension Updater should let global admins choose whether to compute the upgrade plan for the entire farm or just for the main wiki

(cherry picked from commit e9146791ce28f971c9657d641c25f4089db6f1cb)

Conflicts:
	xwiki-platform-core/xwiki-platform-oldcore/src/main/resources/ApplicationResources.properties
XWIKI-10211: Paginate the Wikis and Extensions steps from Distribution Wizard

(cherry picked from commit 9ec7c54ab8d8989ef8277d3a836d635612f56262)