Tidied up and added logging

Tidied up: SimpleDBConsumedStore, UnconsumedFeedEntriesFinder, UnconsumedFeedEntriesFinderTest
Added logging: FeedConsumerImpl, FeedConsumerScheduler, UnconsumedFeedEntriesFinder
REfactoring FeedConsumerImpl
Added FeedEndpoint http response check

It should throw an exception if the HTTP endpoint returns not OK.
Changed FeedConsumerImpl to keep carrying on even if entryConsumer throws exception
Refactored MultipleClientTest

In this instance a JUnit+Hamcrest style test seems more readable
Extracted helper methods to make the main test more readable
Replaced Slow and Fast action with a parametrized DelayedAction (+1 squashed commit)
Squashed commits:
[df0a818] Added test to exploit "forgotten-entry" problem
Changing the store to provide unconsumed entries (+1 squashed commit)
Squashed commits:
[8105f91] Stubbed ConsumedStore#getUnconsumed method
Updated SimpleDBConsumedStoreTest

Added test for method to retrieve entriesToBeConsumed
Refactored existing methods
Fixed Mock initialization in FeedConsumerImplTest
Replaced ConsumedStore type variable with hard type

In one place the generic interface was passed a parameter of a different type. It compiled because in that instance the type variable was left unbound. But at runtime it caused the thread to hang-up without throwing any exception...
The problem was causing the MultipleClientTest to misbehave.
Renamed ConsumedStore to FeedTracker
@Ignore MultipleClientTest for now
Added new EntryConsumer implementation
Updated FeedConsumer
Rewired classes to use new implementation

Changed to accept Links and/or use the new implementation
- FeedConsumerConfiguration
- FeedConsumerScheduler
- EntryConsumerWithMetrics
- FeedConsumerWithMetrics
- PollingActivityHealthCheck
Replaced old implementations
Refactored UnconsumedFeedEntriesFinder (now AvailableFeedEntriesFinder) to add the resource-link to the tracker
Removed underscore from test names
Added test for FeedTracker.track simpleDB implementation; changed AvailableFeedEntriesFinder#isTracked to return true rathen than false
Changed AvailableFeedEntriesFinder, updated FeedConsumerConfiguration and FeedConsumerScheduler

- AvailableFeedEntriesFinder: expects feedEndpoint as constructor parameter rather than method parameter. Now it will be run
  regularly by the scheduler and it's more convenient to encapsulate the feed-endpoint in it
- FeedConsumerScheduler: expects a feedEntryFinder. It will run it using the same interval of the consumer, but earlier.
- FeedConsumerConfiguration: now instantiates the scheduler providing a feedEntryFinder
Updated FeedConsumerSchedulerTest