remove logs about sending alert message
change check time interval method
change frontend code about tag module
change MetricItemConfig model
change backend part for tag module
refactor metric module
change alert type select method in rule ftl, add some descs in ftl, enhance tags' style
Merge branch 'master' of https://github.com/dianping/cat
Merge pull request #527 from leonindy/master

refactor tag module and metric module, amend rule ftl