Sidebar component

In **GAME** and **Admin panel** we use a sidebar for navigation. Originally the sidebar in both tools was the same, but some time ago we improved it in **GAME**. I had some talks with other designers and found that other teams would like to use this UI component in their projects as well.

[I created a draft for the component](https://www.figma.com/file/4kkSm2Y82F05Mbtlb7913z/Wave-snowflakes?node-id=6%3A1786), that was used as the basis for the new design in GAME.

The new version has some additional features on top of simple navigation:

- Switching projects/tools. For example, in **GAME** we have **Rider** space and **Supply** and we need a way to switch to a different space. In Supply there is a similar need to switch between some Driver tools:

- Icons for menu items
- Notification badges: show new items or other information
- Widgets area: for progress bars, or other things that are global.

cc. @phllipo