Persist and rebind feeds

- Adds Feed interface
- Adds abstractEntity.addFeed; if added like that then feed is persisted
- Adds EntityInternal.getFeedSupport(), which has getFeeds(), addFeed(),
  removeFeed() and getAllFeeds()
- AbstractFeed.poller: make private, with getter;
  and make transient
FunctionFeed: test persistence

- and make easier to build a FunctionPollConfig
Test rebinding SshFeed
Persist JmxFeed: testing and transient fields
Experimenting with Feed as EntityAdjunct
Tidy ChefAttributeFeed
fix saveIptablesRules
Convert Feed to extend EntityAdjunct
Adds IllegalStateExceptionSupplier.EMPTY_EXCEPTION

- don’t create a new instance every time a Maybe.absent is constructed
BROOKLYN-55 install script for brooklyn
addressed comments for saveIpTablesRules
Adds persister.loadMementoRawData

- Refactors BrooklynMementoPersisterToObjectStore to remove duplication
- Adds BrooklynMementoRawData, which has the contents of the raw
  blobs/files for persistence (rather than deserialised mementos)
- Adds BrooklynMementoPersisterToObjectStore.loadMementoRawData
- Adds BrooklynMementoPersisterToObjectStore.checkpoint(BrooklynMementoRawData)
copy-state CLI: use BrooklynMementoRawData
CLI copy-state supports uploading to any location

- previously could only copy to the filesystem, rather than to
  any object store
Transformations of persisted state
CLI copy-state: support transformations
Transformations of BrooklynMemento (persisted state)
Move PerformanceTestUtils from core to usage/test-support
Adds load tests

- testing number of concurrent apps that can be started, and number
  of apps that can be managed.
Adds support for deploying the visitors example app, backed with Riak