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
Move support file about spec to /spec/support directory

Generally, support files about spec should be located in /spec/support
Add admin user factory and fix contestant user factory
Use build method instead of create method
Fix and add specs
Add UserController spec
Fix contest factory and add contest model spec
Add ProblemController spec
Rename factory names and improve some controller specs
Remove redundant empty line
Merge pull request #100 from murooka/enhance_specs

Enhance specs
Modify seed to create numbered groups with argument
Add usage of `rake db:seed groups=N`
Merge pull request #121 from TakenokoChocoHolic/120_numbered_group_seed

120 numbered group seed
Update .gitignore