* Change graceful to use a singleton obtained through GetManager instead of a global.
* Graceful: Make TestPullRequests shutdownable
* Graceful: Make the cron tasks graceful
* Graceful: AddTestPullRequest run in graceful ctx
* Graceful: SyncMirrors shutdown
* Graceful: SetDefaultContext for Xorm to be HammerContext
* Avoid starting graceful for migrate commands and checkout
* Graceful: DeliverHooks now can be shutdown
* Fix multiple syncing errors in modules/sync/UniqueQueue & Make UniqueQueue closable
* Begin the process of making the repo indexer shutdown gracefully
* Graceful Shutdown for windows and others
Restructures modules/graceful, adding shutdown for windows, removing and
replacing the old minwinsvc code.
Creates a new waitGroup - terminate which allows for goroutines to
finish up after the shutdown of the servers.
Shutdown and terminate hooks are added for goroutines.
* Remove unused functions - these can be added in a different PR
* Add startup timeout functionality
* Document STARTUP_TIMEOUT
