add AppMaster fault tolerance
revert status manager
add Post and Get application data
fix ClockService bug
refactor the Log format
Merge remote-tracking branch 'upstream/master'
revert ClockService change
fix ClockService
refactor code
minor fix
refacor interface
refine AppDataStore interface
extract AppDataStore implementation from AppMaster
delete StorageManagerFactory
remove AppDataStore Update verification
Merge pull request #95 from huafengw/master

add AppMaster fault tolerance
close checkpoint manager when closing StorageManager
Merge remote branch 'upstream/master' into exact_once