* Add the class "pad" to the `<html>` tag in `pad.html` (the outer
iframe's parent).
* Change the CSS selector that refers to the `<html>` tag in
`pad.html` from `html:not(.inner-editor)` to `html.pad`.
* Change the class name of the outer iframe's `<html>` tag from
"inner-editor" to "outer-editor".
* Update CSS rules to use the new class name.
Until now, the "mobile layout" (with right toolbar on bottom of the screen) was displayed only when screen was smaller than 800px. It made the toolbar break for screen about 1000px when a lot of plugins are in the toolbar.
Now instead, we detect with javascript when the toolbar icons overflow the natural space available, and we switch in "mobile layout" in such case
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
