fix accessibility issues as presenter

.../imports/ui/components/captions/writer-menu/component.jsx

...omponents/presentation/presentation-toolbar/component.jsx

...presentation/presentation-toolbar/zoom-tool/component.jsx

.../ui/components/user-list/captions-list-item/component.jsx

...orts/ui/components/user-list/chat-list-item/component.jsx

...orts/ui/components/user-list/chat-list-item/container.jsx

...s/user-list/user-list-content/user-messages/component.jsx

bigbluebutton-html5/private/locales/en.json