[preview] Change hover and click handling

Adds the preview image to a button, where the clicked signal gets connected for left click.

Buttons are wrapped inside an Eventbox for handling cursor changes.

added 2 commits

• 814f236a - [preview] Change hover and click handling
• b5ab7dd9 - [preview] Update manifest.ini

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added 3 commits

• bef255e5 - 1 commit from branch gajim:master
• d2e8d435 - [preview] Change hover and click handling
• e4c1d26a - [preview] Update manifest.ini

Compare with previous version

merged