feature: (Un)check articles for article sync

[JuliusR]

Status quo

When synchronizing articles with the "external database" (sharedlists), all articles are updated.

Suggestion

I would like to add a checkbox in the beginning of every article row. By using that checkbox, the user can pick those articles that he would like to include for the update. By default, all checkboxes are checked. A checkbox in the table header allows to toggle all checkboxes at once.

Note that the suggested change is minimally invasive because all checkboxes are checked by default.

Here is how it could look like:

Note on outlisted articles

From my point of view, outlisted articles do not need this feature: it should be fine to delete all of them if the supplier does not offer them (any more).

[JuliusR]

I can offer to create a pull request for this.

What are your opinions on this issue?