Add panel padding property

[antis81]

references #909

TODO:

• Add a "padding" parameter in settings dialog.
• Add "inset" to "padding" values.
• Initialize dialog fields. (should be 0)
• Make dialog strings translatable.
• Save value(s) in settings.

[antis81]

FYI: Due to these lines setting the padding on the "outer" QFrame behaves like what is described as "inset" in the QtQuick::Control documentation linked above. Taking this little - important - detail into account and setting the padding on the "inner" QFrame the behavior is exactly as expected and the panel contents start to "shrink"… 🎉

[antis81]

@stefonarch Functionality is complete. From what I remember giving negative numbers allows for "floating" panels in LXQt (similar to KDE's panel). It adds a little bit flexibility for customization. Please let me know if and what you need for translations. Initialization I don't know if that is even required and I don't have the time to build and test this.

[stefonarch]

Padding works. It's results are similar to "icon size" and other configurations in the final result.

panel2.mp4

The worldclock plugin goes out of panel instead:

From what I remember giving negative numbers allows for "floating" panels in LXQt (similar to KDE's panel).

Not really: Negative pixel value sets the panel length to that many pixels less than available screen space. A floating panel would be (is) a big source of bugs.

[antis81]

To make this fully work, the font (px) size has to be relative the plugin's (icon)…

• …height for horizontal and…
• …width for vertical panel positioning

This is independent from the padding itself and so I don't see it in this PR (requires touching all plugins).