Investigate: Add copy action

[mpourmpoulis]

While in general simply selecting a region and then using default Caster stoosh [<n>] Is very handy and flexible scenes since You can choose which slot do you want to fill , having a quick copy action might not be that bad. Nonetheless, there are a few important questions

• Should these be implemented in the backned or from within the grammar?

• should the text the user wants Be selected or not?

• Behavior with multiple cursors?

• Showing alternatives?