* Implement very basic hashing scheme for the fake crypto layer. We need
  this to avoid having duplicate keys in the database (in particular, in
  the WoT).
* Introduce `Snake.Crypto.Common.compareHashes` for easier testing
  purposes with the fake crypto backend.
* Fix the WoT tests to work properly with the fake crypto backend.
* Prevent duplicate keys in the local network backend.

* Add a model for the Web of Trust entries
* Add insertion of Web of Trust entries on friendship
* Implement friendship using the Web of Trust
* Implement test for the friendship using Web of Trust

* Add support for real/fake crypto backend and local/remote network
  layer.
* Update the fake crypto layer.
* Introduce `Snake.Model.ModelBase.fetchAll`, the Promise verision of
  the `ready` event.
* Introduce support for the `reset` raven primitive, a debugging feature
  to completely clean the database.
* Introduce two new group-related tests.
* Introduce a simple stateful performance collection framework using
  `LocalStorage`.

* In detail: now when a friendship is made, the friend is added to our
  default group (which will contain all and only our friends).
* Refactorize the group creation: now is done by the method setupNew of
  the Snake.Model.Group instance, instead of replicating the code every
  time; this also provides UI decoupling.
* Add tests for groups
* Implement option passing to the model when creating collections.
* Implement more generic testing functions

* Reintroduce the `isMyDuty` approach to detect which class is
  responsible for a certain incoming object
* Let users of `Snake.Model.Group` specify how many messages they want
  to fetch
* Let message fetch in `Snake.Model.Group` depend on `address`
  availability, not on `id`
* Properly detect whether an incoming "message" is a
  `Snake.Model.Message` or a `Snake.Model.Post` depending on the
  associated address
* Add `address` to the `group-joined` message

* Emit a warning in case of failure
* Make `Snake.Model.SessionUser.processNewMessages` return the new
  messages, mainly for easier testing
* Let the login fail in case we weren't able to decrypt the user
  descriptor

This commit is a workaround for a bug in the WebCrypto API
implementation of Firefox.

* Introduce the `locked` function, which wraps in a `PromiseQueue` an
  arbitrary function definition
* Wrap all the functions in `Snake.Crypto.Common` using `importKey` in
  `locked`

* Implement tests
* Fix a bug in the testing network layer

Firefox throws errors in case WebCrypto API `importKey` and `sign`
operations are mixed together from different workflows. We implmeneted a
queue using Promise to ensure two related `importKey` and `sign`
operations are always performed sequentially.

All tests now pass sucessfully on Firefox. Tested on Firefox 42 and
nightly.

* s/.target.result//
* Specify possible usages when importing a key
* Do not serialize keys in ArrayBufferViews, use JWK or CryptoKey
* Add support for converting only the private part of a key in
  `privateKeyToJwk`
* Don't give out raw ArrayBufferView, convert them to Uint8Array
* Update parameters to the standard WebCrypto API interface
* Update fhmqv.js, sessionuser.js according to the changes above
* Update config.js, use SHA-1 for Firefox compatibility and add
  `namedCurve` to `signAlgorithm`

Now all the network related stuff is isolated in Snake.Network, this way
we'll be able to implement a fake storage server on the client side for
easier testing.