XWIKI-13735: Some special characters in request parameter keys cause a "missing end delimiter" exception

* minor improvement

* Render the section title using the plain syntax. We can't change the DocumentSection class to hold the plain title instead of the raw wiki syntax because it is exposed in the public API.

* Simplify how the image is vertically aligned.

XWIKI-13663: Update the User Profile's "Dashboard preferences" label to be in line with its behaviour

XWIKI-13663: Update the User Profile's "Dashboard preferences" label to be in line with its behaviour

* Add the width and height parameters and remove the hard-coded width/height from the CSS
* Add also a 'class' parameter to be able to add additional CSS classes.

XWIKI-13087: The setup of user initial groups on user creation can set groups cache to a wrong value, resulting in wrong user groups until next restart

XWIKI-13716: On Administration rights page, radio button is not stick at "users" when I resize my browser

XWIKI-13715: XWiki#getPlainUserName() should log only a warning instead of an error with full stack trace because it falls-back on the user profile reference name
* Improve warning message.

XWIKI-13715: XWiki#getPlainUserName() should log only a warning instead of an error with full stack trace because it falls-back on the user profile reference name

XWIKI-13710: The title displayed for the current document in the navigation panel is "Document Tree"
* Actually the display script service doesn't help. Using the default displayer hint is not good because the documents that have a sheet associated (the BlogIntroduction) are badly displayed. We need to use the sheet displayer but we need to make sure the displayed document instance is different than the current document (and we can achieve this through clonning).

XWIKI-13712: Document#saveDocument set the document author as guest reference instead of null when context has no user

XWIKI-13712: Document#saveDocument set the document author as guest reference instead of null when context has no user