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.

.vimrc

@@ -1,6 +1,9 @@
 " Ensure certain plugins work by removing vi compatable modes
 set nocompatible
 
+" Make backspace work as expected on all platforms
+set backspace=indent,eol,start
+
 " Start Vundle, temporarily set some values
 set rtp+=~/.vim/bundle/Vundle.vim
 filetype off