On pick sheet, if user has picked a game already, display their pick instead of buttons.

* Add Pick#text (e.g. TOR +2).
* Add User#pick_for(game).
update README
Improve CSS on picks page.

* Remove table and replace with Bootstrap span2's.
* Use SCSS @extend so we can have semantic class names.
* Fix the width of the pick buttons to 75px.
When game's score is updated, decide all associated picks.

* Game has_many :picks.
* Add decide_picks as an after_update callback to Game.
* Change User factory to use sequences, so we can make multiple picks in the unit test.