XD-2332 Server-Side CronExpression Validation

* Add validation REST endpoint
* Add AngularJS directive to perform async validation

XD-2332 Code Review Changes

* Add integration tests for ValidationController
* Rename `CronValidationDto` to `CronValidation`
* Move `CronValidation` to REST domain module
* Improving Async Validation
XD-2377 Dynamic release links in UI "About" page

* Provide XD version info via `/management/info`
* Add AngularJS service to retrieve version info
* Add version info to About page

XD-2377 Code Review Changes

* Add integration test
* Create a dedicated `VersionResource` class
* Add `VersionController`
Fix Assert in VersionResource
XD-2429 Bind Producer Before Consumer

JIRA: https://jira.spring.io/browse/XD-2429

When tapping a fire hose, it was possible to get `Dispatcher has no subscriber`
errors on the first module's `output` channel.

This was because the `AbstractMessageBusBinderPlugin` bound the consumer (`input`)
first and messages start flowing before the producer (`output` is bound.
If the output channel is a `SubscribableChannel`, `Dispatcher has no subscribers`
resulted.

Change the bind order so that the output channel is bound first, then the
inbound channel. Similar to the way we bind modules right-to-left when using
a `LocalMessageBus`, we need to bind the module itself right-to-left.

This is only a problem when a stream starts with a tap because, with a "normal" stream,
the last module to be bound is the source, and we don't start it until the source itself
is bound; hence no messages flow to the downstream processors so it doesn't matter what
order their channels are bound.

With a tap, messages can start flowing from the tap as soon as the input channel is bound to the bus.
XD-2120: Allow file based conf of users and ROLES
XD-2377-2 Add `$scope.$apply` to `about` controller
XD-2331: Single node recovery on disconnect

When a single node server disconnects and reconnects to ZK
(for instance when running on a laptop that goes to sleep)
the leader election routine was failing an assert because
the CuratorFramework was not in STARTED state. This was
happening because the container listener forces a client
shutdown and reconnect to guarantee that all its ephemeral
nodes are cleaned up. This connection is the same one
being passed to the leader election routine.

The fix is to only force the container to recreate the
CuratorFramework if it is not in the STARTED state.
The state transition of SUSPENDED -> LOST -> RECONNECTED
where the framework has restarted seems to happen
consistently when the machine running the process
goes to sleep and wakes up.

XD-2373: Distributed test should verify container shutdown

After each test, block execution until admin indicates that
all containers have been unregistered from ZK.

Destroy streams before container shutdown

Increased state transition timeout

Some tests require deployment to a container after it joins
the cluster. Since there is a mandatory waiting period before
new containers are assigned deployments (15 seconds by default)
the wait period for the verify stream/job state methods has been
increased.