JWK creation from a shared secret

[Spomky]

Q	A
Branch?	v1.1
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Fixed tickets
License	MIT
Tests added	Yes
Doc PR	web-token/jwt-doc#1

This PR adds a new method to the JWK Factory (web-token/jwt-key-mgmt).
It is now easier to create a JWK from a shared secret:

$jwk = JWKFactory::createFromSecret('My Secret Key');

The bundle can also take advantage of this new method:

jose:
    keys:
        my_share_key:
            secret: # New key type
                secret: 'This is my secret'
                additional_values:
                    use: 'sig'
                    alg: 'RS512'
                is_public: true

[coveralls]

Coverage decreased (-0.07%) to 86.039% when pulling 314438d on KeyFromSecret into a1b60e8 on v1.0.

[coveralls]

Coverage increased (+0.3%) to 86.45% when pulling 36d7e01 on KeyFromSecret into 52a12b6 on v1.1.