fix #223: nnoremap instead of noremap

- mapping operator-pending-mode and selection-mode has undesirable
side-effects, and isn't actually used by jedi-vim.
- also, wrap 'for' loops in s:init() functions to avoid polluting the
global namespace ('for key in keys' assigns g:key).
Merge pull request #225 from justinmk/master

fix #223: nnoremap instead of noremap