various nvim/tmux updates

* make sure diffs open vertically in vim
* update tmux theme
* allow tmux to change the title of the terminal
* add .nvim/shada to gitignore ?

nvim/nvimrc.symlink

@@ -111,6 +111,8 @@ set clipboard=unnamed
 " faster redrawing
 set ttyfast
 
+set diffopt+=vertical
+
 " highlight conflicts
 match ErrorMsg '^\(<\|=\|>\)\{7\}\([^=].\+\)\?$'