topic create, show and list.
add topic feature test.
create topic reply, list replies.
add topic reply feature test.
upload photo of topic and reply, its content can be markdown.
show time distance.
add index.
remove unnecessary pending.
add encoding: utf-8.
limit sms to 100 words.
Merge pull request #397 from saberma/saberma-enhancement/adjust-sms-limit

活动变更内容字数限制为100字
Merge pull request #395 from saberma/saberma-feature/383-mini-bbs

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merge master.
upgrade capybara to fixed:      Capybara::Ambiguous:
       Ambiguous match, found 2 elements matching button "获取短信校验码"
test system notfication.