XWIKI-10164: Step buttons are enabled if you reload the page or access the Distribution Wizard while the installation is in progress

(cherry picked from commit 4249358421de56e7db3ae5b7c5fa2cef50e23bab)
XWIKI-9595: Ask confirmation for pages not needed anymore before deleting them

(cherry picked from commit 5cdc5d047867a6e34ee887bcd8925116e1009fe1)