Separation of download/upload in thread

To speed up the interaction with the user, it executes the downloading
and uploading in another thread.

re #6894
Merge branch 'feature/6176_upload_scripts' into feature/6894_responsiveness_script_repo

This was necessary to allow us to speed up the interaction with the upload
and fetch the changes on download as well.

re #6894
Add a new icon for the ScriptRepository

re #6894
Show the icon of running processing

This helps the user to identify that download and uploading is running.

re #6894
Solve warnings at cppcheck for ScriptRepositoryImpl

re #6894
Merge branch 'feature/6894_responsiveness_script_repo'