This reverts commit 869042d6.

* Keep only one category opened at once
* Expand the selected category on the server side to avoid flickering UI on page load.
* Fix the menu when the Panels section is active.

* Avoid trailing whitespace in link and button labels because some functional tests use these labels to locate the links/buttons.

* Disable the left/right panel inputs when the corresponding column is hidden, in order to not loose the panels configuration.

* Update functional tests.

- moving the horizontal menu burgers on the left, to avoid confusion between the drawer menu and the horizontal menus

* Display the menu using Bootstrap's Accordion (collapsible menu)
* Fix the icons for some of the categories.
* Remove CSS and JS that is not needed anymore
* Add missing section description.

* Small improvements to the Users & Rights sections.

* Improve the Look & Feel sections
* Move panel related configuration to the Panels section
* Show the Page Layout section first and then the Panel List (in the Panels section)
* Rename the Presentation section into Themes, and keep only the Color Theme, Icon Theme and Skin (for now)
* Rename the Elements section into Presentation, with Page Tabs, Header and Footer
* Add hints.

* Improve the sections from the Other category.
* Move Invitation and User Directory sections to the Users & Rights category
* Move Application Panel section to the Look & Feel

* Add a new category "Editing" with the following sections: 'Edit Mode', 'WYSIWYG Editor' and 'Syntaxes'.
* Move the default syntax configuration to the Syntaxes section.
* Move the default WYSIWYG editor configuration to the WYSIWYG Editor section.
* Place the Editing category in the right order.
* Remove the old 'Configuration' category that remained empty.

* Improve the style of the displayer.

* Make the notifications counter red.

* Improve translations.

* Improve translations.

* Improve the Mail section.
* Rename General section to Advanced. Add help text to the mail status section. Place the Mail section in the right order.

* Add a Search category with two sections: Search and Search suggest
* Improve the existing Search and Search Suggest sections

* Minor rewording

* Minor rewording

* Improve the Wikis category and its sections.
* Rename "Template" in "Wiki Templates" and add help text
* Use the full width in the Descriptor section