Module switcher

[saengel]

Description

Module switcher first pass for modularization

Code changes:

1. s2.css - Styling for the new <DropdownMenu /> generic component, and all of its sub-components. Small shifts to existing code for .interfaceLinks-options to enable compatibility with the existing language menu dropdown and the new generic dropdown, mostly with using flex for text alignment & switching between languages, as opposed to setting text-align
2. static/js/common/DropdownMenu.jsx - A new file containing a generic dropdown menu (to be reused in the future) that's able to render children as a composable component. Heavily based on the existing code for <InterfaceLanguageMenu /> in Misc.jsx. The subcomponents are re-usable as well.
3. static/js/Header.jsx - Added the module switcher next to the language toggle, with the implementation configuration of the composable components in such a way to meet the specs of this specific project.
4. Added the specific icons needed for the specific implementation of the module switcher.

Notes:

• Once sheets vs library internal state is confirmed, the logic around opening links will have to be slightly modified to enable conditional opening in a new tab.