modify model

Conflicts:
	app/models/problem.rb
Add some methods to model and remove unused fields

Conflicts:
	app/models/problem.rb
Modify view and controller to adapt to model

Conflicts:
	app/controllers/contests/problems_controller.rb
	app/views/contests/problems/index.html.erb
Remove unused file
Fix some bugs
Remove unused comment
Fix submission history
Refactor User model
Add Attendance model
Remove docs. Close #93
Merge branch 'master' into 93_remove_docs
Merge pull request #103 from murooka/refactor_model

Refactor model
Fix bugs of creating Submit record and submission history.
Fix a bug of scoreboard. Fix time format. Close #88
Remove a redundant space.
Merge pull request #104 from TakenokoChocoHolic/93_remove_docs

Remove docs. Close #93
Merge pull request #106 from TakenokoChocoHolic/fix_bugs_of_refactoring

Fix bugs of creating Submit record and submission history.
Change spec setting

* Watch spec/*.rb and spec/factories/*.rb by guard
* Enable to use factory_girl in spec
Add spec to check seeding before running spec
Add factory code and rewrite spec with factory_girl