non-freshing join
1,redirect to login page while click "join" button.
2, refresh count of joined.

know issue:
  1, while no guys joined an event, this first guy click "join" button, the "Joined guys" section should not shown.
  2, avatar section could not refresh after someone joined.
1, cancel a joined event.
2, read tooltip text from i18n.
优化代码
add js testing for asyn event joining.
Merge remote-tracking branch 'richard-ma/master' into translation/en
use angular services to reload participated users.
support capybara javascript feature test.
fixed rspec error. add angular services test.
Merge pull request #329 from saberma/saberma-feature/319-join-with-no-fresh

报名后更新「已参加用户」 #319
add homepage feature description. close #320
Merge pull request #335 from saberma/saberma-enhancement/320-homepage-describe-slug-and-follow-feature

首页增加特色描述 #320
event display end. fix #330
Merge remote-tracking branch 'upstream/master' into feature/330-event-display-end
event display end 2.fix #330
Merge pull request #328 from saberma/translation/en

英文版本翻译
Merge pull request #338 from ebowsoft/feature/330-event-display-end

event display end. fix #330
it should return to event page after sign in. fixed #339
merge.
use sendgrid.