[multi-sources-removal] Simplify ConnectionsSet internal structures and public methods since it now handles a connection to the system source only Related to #2919300 [jcr: adjust 3.17.11 migration, fix a number of bugs in new ConnectionsSet implementation, fix source.{open,close}_source_connections]

* {
  color: #000 !important;
}

div#popupLoginBox,
div#popupLoginBox,
img#logo, div.header,
#navColumnLeft, #navColumnRight,
#footer {
  display: none
}

div#pageContent{
  border: none;
}