Display spinners while geogebra, video, and audio elements are loading

docs/release-notes-player.txt

projects/common/components/geometry/geometry.component.ts

projects/common/components/media-elements/audio.component.ts

projects/common/components/media-elements/video.component.ts

projects/common/components/spinner/spinner.component.ts

...on/directives/media-player-element-component.directive.ts

projects/common/shared.module.ts