css: refactor element positioning

No more javascript to change css properties
Remove a number of useless tables
Try to stop positioning elements with absolute, but use flex-boxes instead

Adds comment to pad template, and move popups and chatbox inside editorcontainerbox (so absolute positioning is straightforward)

Make the design more consistent: always use base color, font-family and font-size. USe relative font size if necessary (.9rem instead of 11px for example)

Remove two columns in the popups, just use one column

Remove css meant to support old browser (like -webkit-box-shadow, -moz-box-shadow). Those css rules are quite common now, and If we want to support very old browser, we should use clean-css or other tools to add them automatically

src/static/skins/colibris/src/components/chat.css

@@ -110,5 +110,5 @@
     right: 0;
   }
 
-  #titlesticky { display: none; }
+  .stick-to-screen-btn { display: none; }
 }

src/static/skins/no-skin/pad.css

@@ -1,5 +0,0 @@
-@media (max-width:600px) {
-  #sidediv {
-    display: none !important;
-  }
-}