optimize loading of vim plugins

[BlueDrink9]

env/Functions takes 20
native ftoff takes 30
xolox/misc/path takes 15, /escape takes 20
nerdtree/uiglue takes 26
syntastic/util takes 13

vimtex!
lazy for gundo window, buffexplorer window

After loading buffer:

tabline.
Airline takes 80 ms, inc 40 for async.vim, 40 for formatter
Native syntax plugin takes 50
xolox misc takes 35
xolox session is 20
airline tabline is 20