ENH: reputation for revision obj

1. Update `Thumbs` model to generic
2. add `reputation` field to Revision model
3. overwrite admin actions in Thumbs model
4. `update_reputation()` model method to update `reputation` field
5. `set_reputation()` can be used to reset reputation field. Can only be
used from command line and not used anywhere in code
6. `.spc-popover` class for bootstrap popover
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. add new fields to haystack search_indexes
3. Filter "tag" search based on score and reputation
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

icon float right
Used in ".accordion-group" to toggle sections
ENH: moderation settings for thumbs obj

Create `enable_reputation` field in attached objects to thumbs
Voting is possible if field set to True