How it works:
_ within the "sideblockheading" a DIV with class="hide-show" holds a link calling the JS containerDisplaySwitching(). To the user it's represented by the icon "switch.gif" (a plus in a square) at the right end side of the header.
_ all content of the sideblock is surounded by a new <div class="blockcontent" id="'.$attributes['id']."_cont\">"
_ a call of the JS containerDisplaySwitching() changes the state of the appropriate DIV with the content to "display:none/inline" and writes this state into a cookie.
_ at the end of every block I added a call to the JS "containerDisplaySet()". This reads the block's state and hides the content or leaves it visible with every page load.
_ in the stylesheet I added the positioning of the icon:
.sideblockheading .hide-show {
float:right;
}
.sideblockheading a img.hide-show-image {
padding-top:0.25em;
}
