Added option to use modal component without header border

...ml5/imports/ui/components/audio/audio-modal/component.jsx

...html5/imports/ui/components/audio/audio-modal/styles.scss

...on-html5/imports/ui/components/lock-viewers/component.jsx

...tton-html5/imports/ui/components/lock-viewers/styles.scss

...on-html5/imports/ui/components/modal/simple/component.jsx

...tton-html5/imports/ui/components/modal/simple/styles.scss

...n-html5/imports/ui/components/video-preview/component.jsx

...ton-html5/imports/ui/components/video-preview/styles.scss