Disabled background painter causes ghost images

[Frenkii]

Describe the bug
When toggle the Enabled button for Date Line the overlays for i.e. active FIRs seems to stack

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Preferences, disable Background'
2. Click on 'Date Line Enable toggle button and toggle i.e. 10 times'
3. Observe the map when clicking again and again

Expected behavior
Only toggle the option and not stack the overlays on the map

Screenshots

[Frenkii]

after moving the map:

[marvk]

@Frenkii this should only happen when the background painter is disabled or a transparent color is set to it.

Each frame is painted completely from scratch and starts by painting the whole canvas with a big rectangle, which will form the ocean area after the land is painted on it. If that rectangle isn't painted, the last frame will stay on the canvas as a ghost image.

The toggle to disable the background painter, just like all painter settings, are currently generated automatically. In reality, it makes no sense to make the background disableable, so I will remove this toggle at the latest along with cleaning up the whole preferences dialog (#26).