Implementation of the JWT policy

[lusoalex]

We added some comments (explain ssh-rsa modulus & exponent)
Remove useless class replaced by Java 8 native classes.

[brasseld]

Several things:

1. Please rebase commits to keep a single commit only (initial implementation of ... blablabla)
2. Let's try to add this unit test:

    @Test
    public void test_with_cache_enabled_and_no_cache_resource() throws Exception {

        String jwt = "jwtUsedAsKeyCache";

        HttpHeaders headers = new HttpHeaders();
        headers.add("Authorization", "Bearer "+jwt);
        when(request.headers()).thenReturn(headers);
        when(configuration.isUseValidationCache()).thenReturn(true);
        when(configuration.getCacheName()).thenReturn(CACHE_NAME);

        //Mock cache actions.
               when(executionContext.getComponent(ResourceManager.class)).thenReturn(resourceManager);
        when(cache.get(jwt)).thenReturn(element);
        when(element.value()).thenReturn(Instant.now().plusSeconds(7200));

        new JWTPolicy(configuration).onRequest(request, response, executionContext, policyChain);

        verify(policyChain,Mockito.times(1)).failWith(any(PolicyResult.class));
        verify(policyChain,Mockito.times(1)).doNext(request, response);
    }

I'm not sure it's an expected behavior 😉

1. Remove target/classes from git

[brasseld]

A new PR has been created from this PR to follow conventions from CONTRIBUTING documentation: #2