deleted useless code:

* src/logos/shared/storage/containerstore.js
* src/logos/shared/storage/storageobject.js
added some documentation to logos.common.preconditions
refactor: renamed logos.command.CommandContext to
logos.command.CommandExecutionContext
added logos.model.State

* logos.model.State provides an instance of the model
* replaced usage of of logos.command.CommandExecutionContext in
  CommandSetApplier with a logos.model.State
* logos.model.State proxies calls to version provider
updates logos.model.VersionProvider to be initialized with the version
.gitignore: added private directory
added spec.helpers.matchers.Promises for help with writing Promises specs
rewrote base storage classes to use goog.Promises

* added logos interface logo.storage.mechanism.Mechanism
* updated InMemoryMechanism to implement logo.storage.mechanism.Mechanism and
  use promises for return values
* updated MessageStorage to reflect changes to the mechanism layer
* updated all specs accordingly