add acts_as_follower gem.
show follow button.
add angularjs-rails gem.
user follow event.
add angular jasmine test.
send email to followers when event create.
add follow hint.
automatic follow event when user join event.
fixed travis-ci error.
add travis-ci before_install config.
try to fix: jasmine can't connect firefox.
update jasmine gem.
revert update jasmine gem.
Merge pull request #306 from saberma/saberma-feature/292-use-can-follow-events

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