reduce db probes for getAvailableActions; simplify SaveUsernames

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

...ton-html5/imports/ui/components/actions-bar/component.jsx

...ton-html5/imports/ui/components/actions-bar/container.jsx

...components/actions-bar/create-breakout-room/container.jsx

...rts/ui/components/actions-bar/desktop-share/component.jsx

.../components/actions-bar/quick-poll-dropdown/component.jsx

...button-html5/imports/ui/components/actions-bar/service.js

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

...n-html5/imports/ui/components/breakout-room/component.jsx

...n-html5/imports/ui/components/breakout-room/container.jsx

...tton-html5/imports/ui/components/breakout-room/service.js

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

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

bigbluebutton-html5/imports/ui/components/chat/service.js

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

...ebutton-html5/imports/ui/components/polling/container.jsx

...utton-html5/imports/ui/components/user-list/component.jsx

...utton-html5/imports/ui/components/user-list/container.jsx

...uebutton-html5/imports/ui/components/user-list/service.js

...s/ui/components/user-list/user-list-content/component.jsx