HttpServeShellCmdtHandler and http server changes

Adding HttpServeShellCmdtHandler to handle  Distributed Shell Command
Moving CommandUtility from reef-websever to helloHttp to share it with
ShellTask
HelloDriver to have all the event handlers
Remove helloTask
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into juwang-httpServerDistributedShell
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into juwang-httpServerDistributedShell
DriverServiceCOnfiguration
Move command utility to common
Use DriverServiceConfiguration
Update HttpServer/JettyHandler
Refactor adn clean up
Merged from master
merge from master
Close the parent context in DefaultContextClosureHandler
The addresses #810 by closing the parent context in `DefaultContextClosureHandler`, if there is any.
Merge pull request #811 from Microsoft-CISL/weimer_810

Close the parent context in DefaultContextClosureHandler
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into juwang-httpServerDistributedShell
Update for review comments
use URLDecoder to decode the request string
Removed APIs deprecated in 0.4

This removes all APIs that have been deprecated oin 0.4 or before.
Merge pull request #813 from Microsoft-CISL/weimer_remove_deprecated_apis

Removed APIs deprecated in 0.4
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into juwang-httpServerDistributedShell
RequestParser update
Update query string parser
minor refactoring in RequestParser: rename it into ParsedHttpRequest;
reformat the code, add finals and do minor optimizations