Bring back the redesigned server tab of the old experimental Tabs v2

The final redesign tries to compromise with people who prefer the desktop-like channel and server list being some kind of sidebar and a flyout. However, in my subjective opinion, the old experimental design with the dock at the bottom was way superior for mobile phone usage.

So instead of offering a half-hearted compromise, Discord should commit to the new UI and offer an optional rollback for people who prefer the old UI.