New feature: copy screens from one clientspace / workspace to another

[drscholly]

Fixes #12

Checklist

• I have read the Contribution Guide ;
• I have read the Contributor License Agreement (CLA) and understand that the submission of this PR will constitute an electronic signature of my agreement of the terms and conditions of DataGalaxy's CLA ;
• There is an approved issue describing the change when contributing a new feature ;
• I have added tests that prove my fix is effective or that my feature works ;
• I have added necessary documentation (if appropriate) ;

Short description of what this resolves:

Changes proposed in this pull request:

• Add new copy-screens command to the toolbox
• It allows to copy screens from a clientspace or workspace to another clientspace or workspace
• Is close to all other features of the toolbox

[drscholly]

Please release v0.4.0 after successful merge

[ggrossetie]

I guess this branch is based on #11 so we should probably merge #11 first and then rebase.

[sailro]

[x] have added necessary documentation (if appropriate) => README.md was not updated for recent PRs, could you make sure everything is up-to-date? (feel free to open a new "documentation" pr if that's more convenient). Thanks!

[ggrossetie]

@drscholly could you please rebase on main branch?