Video group : add to group option should be always available

Description

During action mode, when you select one object (video or group) or more, the "Add to group" option should be always available.

See !739 (merged)

Expected behavior

To be precise :

• one video -> add to an existing group
• multiple videos -> add to an existing group or create a new one
• one group -> add to an existing group (a create action is a rename action)
• multiple groups -> add to an existing group or create a new one (or merge... see #1506 (closed))
• multiple groups and videos -> add to an existing group or create a new one (or merge... see #1506 (closed))

Screenshot / video

App mode

Smartphone

TV