Feature/user crud

# About the pull

This pull request contains:

* Changes relationship between users and positions
* Show and edit user info

# WIP

Integration Testing... (uploading in a few minutes)
it would be useful if you explain why for further reference:

before_action is the same as before_filter but the last is being deprecated in rails 4

https://github.com/rails/rails/blob/master/actionpack/lib/abstract_controller/callbacks.rb#L164