Merge pull request #424 from youyong205/master

refactor alert module
Merge pull request #425 from youyong205/master

refactor
use ftl as alert template, add argument to receiver method
Merge pull request #426 from leonindy/master

use ftl as alert template, add argument to receiver method
Merge branch 'master' of github.com:dianping/cat
modify the default-alert-policy