Restored export as it makes sense in bash

Bash has weird initialization: bashrc is sourced in non-login interactive shell, 
but not in login interactive shell; profile is sourced in login interactive 
shell, but not in non-login interactive, thus exporting in profile does make 
sense. In zsh case zshrc is always sourced when shell is interactive and 
exporting thus makes no sense.
Added setopt promptpercent and promptsubst:

these options are required for powerline to work, but the latter is off by 
default