Add a new concept of "signer" in order to delegate the process of cookie signing, and cookie signature check.
The cookie filter will no more do this work, but delegates signing and signature verification to its injected signer.

Create a DefaultCookieSigner component which use the existing SignatureKey in order to stay compatible with previous releases.
The DefaultCookieSigner get the signature key by dependency injection and use the HMAC-SHA1 algorithm (defined in Crypto class) to sign the cookie.
Merge branch 'signer' of https://github.com/a-peyrard/restx into a-peyrard-signer

Conflicts:
	restx-core/src/main/java/restx/security/RestxSessionCookieFilter.java
	restx-core/src/main/java/restx/specs/WhenRestxSessionHeaderLoader.java
	restx-specs-tests/src/main/java/restx/tests/HttpTestClient.java