[web/debug] Fix check for open sessions
itervalues returns an iterator, which never evaluates to False.
Regression from 0bb18407c053 "[toward py3k] rewrite dict.keys() and
dict.values() (part of #2711624)".
[cwconfig] Remove useless 'ui-cube' configuration option (closes #3728904)
The mechanism introduced could never actually be used as it brings dependency
loops to the cube graph. Just get rid of it.
This reverts commit 4032499c701e.