refactor AlertMesageEntity
Merge pull request #450 from youyong205/master

refactor
Merge pull request #451 from youyong205/master

modify the alert manager
fix paas system monitor bug & optimize
Merge branch 'master' of https://github.com/dianping/cat
add alert suspend feature and alert recover announcement feature
add unit when sending alert
extract method from AlertManager, add alert http api docs
add SuspendTest
resolve conflicts
change test cases
Merge pull request #452 from youyong205/master

fix many bug
Merge pull request #453 from jialinsun/master

fix paas system monitor bug & optimize detail
resolve conflicts
fix bugs
fix issue of date format for third party alert mail content
fix description issue of app line chart
add a little code
Merge pull request #455 from jialinsun/master

fix issue of date format for third party alert mail content
Merge pull request #454 from leonindy/master

add alert suspend and recovery announcement features, add alert http api document