[Website] change getting window width method

[bullet03]

On resolutions between 1025px and 1041px right side menu overlaped left side menu. Reason is in page-nav,js in $(window).width(), which didn't get correct width since it didn't include horizontall scroll width. Used window.innerWidth instead to get correct width.

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[bullet03]

before:

after:

[alevtinaboiko]

Verified, works as expected. Reviewed and tested by QA

[bullet03]

@pcoet, could you, please, review this PR? It is ready.

[bullet03]

@aromanenko-dev, could you, please, help to merge current PR. It was approved.

[aromanenko-dev]

Thanks, merged.