js() mode should set js params to mixed block

[miripiruni]

Test case: https://goo.gl/8LK0IQ

BEMJSON:

([
    { block: 'b', mix: { block: 'mixed' } },
    { block: 'b', mix: { block: 'mixed', js: { test: 1 } } },
]);

Templates:

block('mixed').js()({ test: 1 });

Current result:

<div class="b mixed"></div>
<div class="b mixed i-bem" data-bem='{"mixed":{"test":1}}'></div>

Expected result:

<div class="b mixed i-bem" data-bem='{"mixed":{"test":1}}'></div>
<div class="b mixed i-bem" data-bem='{"mixed":{"test":1}}'></div>

@zxqfox @tadatuta

[tadatuta]

Same as https://github.com/bem/bem-xjst/issues/147