XWIKI-9405: Add a "SubWiki Creation" right.

* I have added the SUBWIKI_CREATION right to the default rights set.
* I have added a check in menuview.vm to not show "add workspace" if the
  current user does not have this new right.
* I have given this new right to the XWikiAdminGroup by default.
XWIKI-9405: Add a "SubWiki Creation" right.

* I have changed DefaultWorkspaceManager#canCreateWorkspace() to take into
  account the new SUBWIKI_CREATION right.
XWIKI-9405: Add a "SubWiki Creation" right.

* I do not show the link "Create Workspace" on the Workspaces Directory if the
  user does not have the right to create a workspace.
XWIKI-9405: Add a "SubWiki Creation" right.

* Fixing the Integration tests.
 XWIKI-9405: Add a "SubWiki Creation" right.

* Fixing the Integration tests.
XWIKI-9405: Add a "SubWiki Creation" right.

* Fixing the Integration tests.
XWIKI-9405: Add a "SubWiki Creation" right.

* Adding changes suggested by committers on the pull request.
** ALL_RIGHTS_EXCEPT_ADMIN renamed ALL_RIGHTS_EXCEPT_ADMIN_AND_SUBWIKI_CREATION.
** deprecatedContext renamed xcontext in DefaultWorkspaceManager#canCreateWorkspace()
** better use of Logger in DefaultWorkspaceManager#canCreateWorkspace()
** introduce $hasCreateSubwiki in xwikivars.vm

Thanks for the review!
Merge pull request #143 from gdelhumeau/XWIKI-9405

XWIKI-9405: Add a "SubWiki Creation" right.