Feature/qa

This fixes a whole bunch of style/convention/etc. issues find by rails_best_practices.

Here's a list of what I fixed from the dev branch:
```
./app/models/user.rb:46 - check 'save' return value or use 'save!'
./db/seeds.rb:9 - use 'create!' instead of 'create' as the latter may not always save
./app/views/solutions/index.html.erb:16 - law of demeter
./app/views/solutions/index.html.erb:17 - law of demeter
./app/views/solutions/index.html.erb:18 - law of demeter
./app/helpers/solutions_helper.rb:1 - remove empty helpers
./app/helpers/problems_helper.rb:1 - remove empty helpers
./app/helpers/profiles_helper.rb:1 - remove empty helpers
./app/helpers/achievements_helper.rb:1 - remove empty helpers
./app/helpers/languages_helper.rb:1 - remove empty helpers
./app/views/problems/_form.html.erb:1 - replace instance variable with local variable
./app/views/problems/_form.html.erb:2 - replace instance variable with local variable
./app/views/problems/_form.html.erb:4 - replace instance variable with local variable
./app/views/problems/_form.html.erb:7 - replace instance variable with local variable
./app/views/solutions/_create_form.html.erb:1 - replace instance variable with local variable
./app/views/solutions/_create_form.html.erb:2 - replace instance variable with local variable
./app/views/solutions/_create_form.html.erb:4 - replace instance variable with local variable
./app/views/solutions/_create_form.html.erb:7 - replace instance variable with local variable
./app/views/solutions/_edit_form.html.erb:1 - replace instance variable with local variable
./app/views/solutions/_edit_form.html.erb:1 - replace instance variable with local variable
./app/views/solutions/_edit_form.html.erb:2 - replace instance variable with local variable
./app/views/solutions/_edit_form.html.erb:4 - replace instance variable with local variable
./app/views/solutions/_edit_form.html.erb:7 - replace instance variable with local variable
./app/views/profiles/_form.html.erb:1 - replace instance variable with local variable
./app/views/profiles/_form.html.erb:2 - replace instance variable with local variable
./app/views/profiles/_form.html.erb:2 - replace instance variable with local variable
./app/views/profiles/_form.html.erb:4 - replace instance variable with local variable
./app/views/profiles/_form.html.erb:7 - replace instance variable with local variable
./app/views/profiles/_form.html.erb:11 - replace instance variable with local variable
./app/views/profiles/_form.html.erb:17 - replace instance variable with local variable
./app/views/languages/_form.html.erb:1 - replace instance variable with local variable
./app/views/languages/_form.html.erb:2 - replace instance variable with local variable
./app/views/languages/_form.html.erb:4 - replace instance variable with local variable
./app/views/languages/_form.html.erb:7 - replace instance variable with local variable
./app/views/achievements/_form.html.erb:1 - replace instance variable with local variable
./app/views/achievements/_form.html.erb:2 - replace instance variable with local variable
./app/views/achievements/_form.html.erb:4 - replace instance variable with local variable
./app/views/achievements/_form.html.erb:7 - replace instance variable with local variable
./app/controllers/achievements_controller.rb:50 - simplify render in controllers
./app/controllers/achievements_controller.rb:66 - simplify render in controllers
./app/controllers/profiles_controller.rb:54 - simplify render in controllers
./app/controllers/profiles_controller.rb:71 - simplify render in controllers
./app/controllers/problems_controller.rb:50 - simplify render in controllers
./app/controllers/problems_controller.rb:66 - simplify render in controllers
./app/controllers/solutions_controller.rb:57 - simplify render in controllers
./app/controllers/solutions_controller.rb:73 - simplify render in controllers
./app/controllers/languages_controller.rb:51 - simplify render in controllers
./app/controllers/languages_controller.rb:67 - simplify render in controllers
./app/models/user.rb:54 - use query attribute (user.email?)
./Capfile:2 - speed up assets precompile with turbo-sprockets-rails3
./app/models/user.rb:9 - remove trailing whitespace
./app/models/profile.rb:13 - remove trailing whitespace
./app/models/achievement.rb:4 - remove trailing whitespace
./app/helpers/application_helper.rb:11 - remove trailing whitespace
./db/migrate/20130212193649_categories_problems.rb:2 - remove trailing whitespace
./db/migrate/20130207192037_achievements_solutions.rb:2 - remove trailing whitespace
./db/seeds.rb:63 - remove trailing whitespace
./config/routes.rb:2 - remove trailing whitespace
./app/controllers/application_controller.rb:19 - remove trailing whitespace
./app/controllers/profiles_controller.rb:63 - remove trailing whitespace
./app/views/users/registrations/edit.html.erb:6 - remove trailing whitespace
./app/views/users/registrations/_compact.html.erb:13 - remove trailing whitespace
```