Rebind split navigation

To tie in with tmux I use <C-htns> to move between splits with <C-u>
 moving to the last active tab.

This has meant shifting some other shortcuts to accomodate.

*  Fuzzy finder is now <C-@> (that's @ = space)
*  Save is now <c-w> rather than <c-s>, and when you save from insert
you stay in insert mode.
*  Tab controls are currently off
Changed leader

Leader is now ` instead of \, largely because \ required a hand move.

Tab navigation is now <leader>h/s with <leader>t to open a new tab