Remove helm-quick-update

It is not needed anymore since helm-candidate-number-limit is
small (less than several thousands). If this is the case, then there's
no difference between quick update and no quick update execution time.
Enabling helm-quick-update makes helm buffer flashing for every entered
character to retrieve new candidate list, which would annoy user.
New documentation on escaping in readme
Fix typos in contribute
separated python settings into a contrib
Add evil-args and evil-jumper to the list of plugins in readme
Add doc for <layer>-excluded-packages variable in readme
Merge pull request #111 from danielwuz/python-contrib

Python contrib
Open `.spacemacs` dotfile in the same manner as init and contrib.