fix bugs which may cause exception
merge newest code
Merge branch 'master' of https://github.com/dianping/cat
add systemRuleConfig page, rename networkRuleConfig page
add system alert task
add default system rule
add alertType: error and warning
merge newest code
Merge pull request #377 from leonindy/master

add system alert task and page
添加所有系统监控指标，重构Agent