fix(ipc): Fallback folder not being user-specific (#2684)

If two users start a bar with IPC and don't have XDG_RUNTIME_DIR set,
polybar will create the fallback directory `/tmp/polybar`.
However, that directory is only accessible by the user that created it
and so polybar running under the second user will fail to open its
socket there.

We add the UID to the fallback directory to prevent this.

Fixes #2683

src/components/controller.cpp

@@ -1,7 +1,5 @@
 #include "components/controller.hpp"
 
-#include <uv.h>
-
 #include <csignal>
 #include <utility>