Add UserTag & UserUserTag Models
Admin can add tags (without autocomplete)
showing UserTag
add autocompletion
Add search module & sending sms to selected group
bug: selecting all checkboxes error
feat: tag guide, turn off resize
feat: add tags from current user data
feat: escape dot from routes used to tag
feat: show users' tags in the user list
feedback: In UsersController, checking validation using @model.valid?"
feedback: using arel table & cleaning spec
feedback: renaming UserTag to Tag
git: merging to develop
git: merging & test
Merge pull request #351 from DonutWorks/feature/issue-320

#320 관리자는 사용자에게 tag를 달 수 있고, 태그별로 sms를 전송할 수 있다.