Implement selected state for left menu entries

User is a bit lost when browsing in side panel because there is no selected state. Only a temporary focus.

Make left panel item look selected even after focus was lost. For instance, after user clicked on the dashboard or a document in a left panel list, the icon doesn't look selected any longer, which can make it difficult for the user to know which icon to click to fold the menu.

Pattern recommendation:

• When a user click on the side panel menu, the menu item should have a "selected state" kept during the navigation, even if the user click on a doc in the list.
• When the user click on another entry menu, the entry menu become selected.
• When the user close the panel, the next item clicked remove the selected state. If it's not doable, closing the panel can flush the selected state.