added title; minor typo fixes
added title; fixed link to configuration
refactored sidebar sections to group related topics together under a section that encompasses what they are about, and communicates to a user that this is the go-to section for provisioning/deploying etc. a druid cluster
Refactored modules section for better flow/readability and added link to extending druid
added title
adjusted size of first section head to match others
Merge branch 'master' into igalDruid
S3Utils: Use RetryUtils from java-util
HttpClientModule: Default http timeout to PT5M
Rework indexing service internals to hopefully be more reliable.

The TaskQueue directly manages the TaskRunner. The main management loop runs
periodically and checks that the runner is doing reasonable things. If not, it
attempts to adjust the runner. The management loop also runs on-demand when a
task is added to keep task assignment relatively low latency. The TaskConsumer
is no longer necessary and so it no longer exists.

Task interval locks are handled differently. Instead of some tasks acquiring
locks at runtime and some tasks having implicit fixed lock intervals, all tasks
ask for locks explicitly. This occurs either in "isReady" (which runs on the
overlord) or in "run" (which runs on the peon).

Other changes:
- The TaskQueue is attached to the leader lifecycle, instead of global
- The TaskLockbox is able to sync itself from storage and is no longer
  bootstrapped by the TaskQueue.
- RemoteTaskRunner does not clean up zk paths until asked to. This will
  prevent deletion of statuses that have not yet been committed.
- Added retries on DbTaskStorage operations.
- Removed SpawnTasksAction (no more subtasks)
- Removed obsolete EventReceiverFirehose configs
- Removed obsolete OldOverlordResource
- Removed TaskStorageQueryAdapter methods related to subtasks
AbstractFixedIntervalTask: Copyright header
TaskQueueConfig: Copyright header
VersionConverterTask: Less goofy import for Preconditions
RemoteTaskRunner: Fix typo
Task interval, isReady hygiene
kafka-eight: bump kafka dependency to 0.8 release
TaskAction: Add JsonSubType for LockTryAcquireAction
IndexTask: Remove unnecessary args to determinePartitions.
IndexTask: Call plumber.startJob()
OverlordResource: Fix comment