refs #2 Add some usefull gems for development and test
refs #2 Change column name of Expenses

category_id -> expense_category_id
refs #2 Relate models between Expenses and ExpenseCategories

and modify factory
refs #2 Use shoulda matcher
refs #2 Improve expenses views for expenses_category

- use radio button
- display expenses category name
- install gems: capybara and launchy
refs #2 Use FactoryGirl for view specs

because some specs require relations of expenses_category
Merge pull request #19 from upinetree/2_relate_expense_categories

2 relate expense categories