Possibility to merge several Game collections

[AndyMCMarks]

Is your feature request related to a problem? Please describe.

I am studying opening ideas throug IA and so I try out several IAs on a specific opening.
Basically 1 series of games played by an IA becomes 1 Game collection.
Since I have several I would like to merge several collections into 1.

Describe the solution you'd like
When building a new collection have an option to include games from other game collections.
( This way you don't need to duplicate the games)

Describe alternatives you've considered
If I want to do it manually i will have to duplicate the games I already entered into a bigger collection, it's a waste of time and a waste of storage ressource.

Additional context
This feature could be used if you want to split&merge games played by amateurs/pro/IAs.