ENH: reputation system for Revision obj

1. change existing scipy_central.thumbs.models.Thumbs to use ContentType
fields
2. Add views, forms, admin interface for POST request of vote (thumbs)
3. client side code is done using Ajax
4. add Reverse generic relatings, model methods in
scipy_central.submission.models.Revision model for reputation system
5. build up-arrow, down-arrow css (used .less, .css is just generated)
ENH: Reputation for comments

There is only "upvote" for comments. Downvote is not allowed
reputation onclick event is directly mentioned in list.html
ENH: order search results based on wilson score

1. New `score` field added to Revision model, which stores wilson, score
confidence
2. allvotes_count, upvotes_count model methods - only count when
is_valid=True
3. add new field to haystack search_indexes
4. Filter "tag" search based on score
ENH: show top-rated in front-page

1. create another tab 'top rated' on front page to show submissions based on score! Filter is created for it
Note: only revision having top Wilson score is showed

2. show all submissions based on score
The above "note" is applicable to [2]

3. create model property in Submission model to get top_revision of the respective submission
ENH: enable reputation for user profile

1. `reputation` field in user profile is present before but never used!
2. reputation for user profile is done as soon as successful voting is
done
ENH: change up and down arrow images

icon-arrow-up --> icon-minus
icon-arrow-down --> icon-plus

Used in ".accordion-group" to toggle sections