add ng-select for templatable select options

- create select-tags component to replace ngx-chips
- create select-options to factorize option selection in forms
- create select-channel to simplify channel selection
- refactor tags validation

shared/models/videos/video-constant.model.ts

@@ -1,4 +1,5 @@
 export interface VideoConstant<T> {
   id: T
   label: string
+  description?: string
 }