Margins control (unify heights & extra margins for widgets)

[luisbocanegra]

Currently there is a padding option that works per widget it, is required to increase/decrease background height for the following cases:

• widgets that set constraintHints = Plasmoid.CanFillArea fill the panel height?,
• margin areas which seem to set widgets at a specific padding set by the theme(?).

There are also widgets that leave too small paddings on the sides this is a problem when there is too much rounding of the widget background.

current version (0.3.0) with no paddings set, just backgrounds filling each widget:

• global menu fills the height
• margin areas on the right have also a different height
• Netspeed widget touches rounded edges

Possible solution

After some experimentation I found out that setting vertical/horizontal margins gets around CanFillArea and margin areas

• [x] Implement global vertical and horizontal margin
• [x] Rename padding to margin
• [x] Make the padding grow with the margins
• [x] Account for vertical panels

[luisbocanegra]

After https://github.com/luisbocanegra/plasma-panel-colorizer/pull/20