add enableDictation prop in settings.yml / bug fixes

bigbluebutton-html5/imports/api/captions/server/methods.js

...n-html5/imports/api/captions/server/methods/appendText.js

...on-html5/imports/ui/components/captions/pad/component.jsx

...on-html5/imports/ui/components/captions/pad/container.jsx

...tton-html5/imports/ui/components/captions/pad/styles.scss

bigbluebutton-html5/private/config/settings.yml