XWIKI-9243: Possible nullpoint in XWikiDocument#getXObjectProperty when asking for object that does not exist
(cherry picked from commit 31b627bda3c4fea07ea661b0548c616f1e2cdfbb)
XWIKI-9253: BaseProperty#setOwnerDocument sets the content as dirty when updating a property
(cherry picked from commit 84c64828717ebe724d7a8b1f44ca49743856d043)
XWIKI-9254: After installing the UI the user isn't taken to the second step of the DW
(cherry picked from commit 79769d13c333cd367496554a515492fab733db51)
Merge branch 'stable-5.0.x' of https://github.com/xwiki/xwiki-platform into xwiki-cs