adds a select random user feature for presenter

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

...tml5/imports/api/meetings/server/methods/setRandomUser.js

...html5/imports/api/meetings/server/modifiers/addMeeting.js

...imports/api/meetings/server/modifiers/updateRandomUser.js

.../ui/components/actions-bar/actions-dropdown/component.jsx

bigbluebutton-html5/imports/ui/components/app/component.jsx

bigbluebutton-html5/imports/ui/components/app/container.jsx

...ml5/imports/ui/components/modal/random-user/component.jsx

...ml5/imports/ui/components/modal/random-user/container.jsx

...html5/imports/ui/components/modal/random-user/styles.scss

...on-html5/imports/ui/stylesheets/variables/typography.scss

bigbluebutton-html5/private/locales/en.json