Implement captions/subtitles

...nfig/edit-custom-config/edit-custom-config.component.html

...config/edit-custom-config/edit-custom-config.component.ts

client/src/app/core/server/server.service.ts

...forms/form-validators/custom-config-validators.service.ts

client/src/app/shared/forms/form-validators/index.ts

...orms/form-validators/video-captions-validators.service.ts

client/src/app/shared/forms/index.ts

client/src/app/shared/forms/reactive-file.component.html

client/src/app/shared/forms/reactive-file.component.scss

client/src/app/shared/forms/reactive-file.component.ts

client/src/app/shared/misc/utils.ts

client/src/app/shared/shared.module.ts

client/src/app/shared/video-caption/index.ts

.../src/app/shared/video-caption/video-caption-edit.model.ts

client/src/app/shared/video-caption/video-caption.service.ts

client/src/app/shared/video/video.model.ts

client/src/app/shared/video/video.service.ts

...+video-edit/shared/video-caption-add-modal.component.html

...+video-edit/shared/video-caption-add-modal.component.scss

...s/+video-edit/shared/video-caption-add-modal.component.ts