In category listing: load 50 items at a time
admin edit pins: paginate 50 items in category search
edit pins: change to edit with button and image

In order to allow multiple selection of items, the edition of the pin is done now through a button or the pin image.
edit pins: edit only through the button, not image.
edit pins: Select and Unselect all pins
edit pins: Button to delete selected pins
Add an option in admin to remove items from categories
Fix pagination in category selection
Add an option in admin to remove items from categories
Update settings.py

Set SEARCH_PINS to false to prevent site pins from appearing in the search results.
Merge pull request #120 from camilotorresf/fixes

Fixes for pagination and category selection/deselection
Update settings.py

Added console handler for logging, set log level to debug and enabled it for modules
Revert logging code
Modified API methods that removes profile photos and backgrouns and method that upload new background fo removing their likes and comments from database
Changed the way environment variables are accessed in settings, to see if it will help to build readthedocs
Accessed all env variables via get
Added API method which allows to Like/Unlike Pins, refs #328
Improved dotdict utils method so it does not throw exceptions, related to misssing key
Updated index page, returned list of pins.
Migated PinLine/Unlike to api method, refs #328