change float price to integer price_in_cents.
add priceable gem.
fixed price change error.
fixed error: move value from price to price_in_cents.
merge master.
sign up directly, but still needs apply to organize events
fix navbar's css, move it into a standalone file for better extend
Merge pull request #481 from saberma/saberma-enhancement/474-use-price-in-cents

使用整型字段来保存金额
Merge branch '418-remove-apply-sign-up' of github.com:jasl/19wu into jasl-418-remove-apply-sign-up
Merge branch 'navbar-style' of github.com:jasl/19wu into jasl-navbar-style