Unselect entries in the main table and opacity of disabled icon-buttons

[k3KAW8Pnf7mkmdSMPHz27]

Is your suggestion for improvement related to a problem? Please describe.

1. At the moment you can't unselect bib entries in the main table. This is perhaps a useless feature but it is part of my "default behaviour". If I am editing a bib entry in a small library, and I want to close the entry tab I click on an empty row in the main table, and I expect the bib entry to be unselected and the entry tab to hide (since there is no longer a selected entry to edit). Am I the only one that repeatedly does this ? 😬
2. On a related note, should disabled icon-buttons change opacity, e.g., if no bib entry is selected.

Additional context
Regarding disabled icon-buttons,

.icon-button:disabled {
    -fx-opacity: 0.4;
}

Looks good to me.

vs

[tobiasdiez]

I think both ideas are good. Would you mind creating PRs for them? (we already have ActionHelper.needsEntriesSelected so this should be straigthforward)

[k3KAW8Pnf7mkmdSMPHz27]

Great!
I'll split it over two PRs. One dealing with the opacity/disabled, which should be finished quicker, and one trying to figure out when it is reasonable to "lose" a selection.

[JavuesZhang]

Hi! Does this issue still accept pull request?

[k3KAW8Pnf7mkmdSMPHz27]

@JavuesZhang, if it is still a problem in the latest version, yes. I unfortunately haven't had time to look at the issue.