Minor tweaks to dunst, vim, zsh

Auto-init tab completion in ZSH
Normalize backspace handling in vim (for windows support)
Force dunst to place notifications on monitor 1, since I moved to
two-monitor setup.

.config/dunst/dunstrc

@@ -1,7 +1,8 @@
 [global]
     geometry = "600x20"
     shrink = no
-    follow = mouse
+    monitor = 1
+    follow = none
     indicate_hidden = yes
     transparency = 0
     frame_width = 2