PLT-5080 (Server): Channel-Admin level permissions (#4874)

Adds permissions for manage/delete public/private channels at the
Channel Admin level.

api/channel.go

@@ -804,11 +804,11 @@ func deleteChannel(c *Context, w http.ResponseWriter, r *http.Request) {
 
 		// Allow delete if user is the only member left in channel
 		if memberCount > 1 {
-			if channel.Type == model.CHANNEL_OPEN && !HasPermissionToTeamContext(c, channel.TeamId, model.PERMISSION_DELETE_PUBLIC_CHANNEL) {
+			if channel.Type == model.CHANNEL_OPEN && !HasPermissionToChannelContext(c, channel.Id, model.PERMISSION_DELETE_PUBLIC_CHANNEL) {
 				return
 			}
 
-			if channel.Type == model.CHANNEL_PRIVATE && !HasPermissionToTeamContext(c, channel.TeamId, model.PERMISSION_DELETE_PRIVATE_CHANNEL) {
+			if channel.Type == model.CHANNEL_PRIVATE && !HasPermissionToChannelContext(c, channel.Id, model.PERMISSION_DELETE_PRIVATE_CHANNEL) {
 				return
 			}
 		}