This patch introduces a live brush preview to the brush editor. The goal of it is to see a live view of your brush when you are changing your settings. You can do the following:

1. move the brush preview around
2. zoom to 100% to see it at full view
3. reset the brush view to see the whole brush centered

There are two engines that gave issues, so I have text in the preview area if they are selected (quick brush and shape brush). The shape brush gave bad artifacts that messed up other brushes. The quick brush did not show a preview, so I decided that it wouldn't get one.

Tested on Windows 10 and KDE Neon.

1. Play around with different settings. Some settings will update the preview as you are using the slider. Other settings only update after the slider is released. These events are controlled by the sigsettingschange the resource manager emits.

2. Changing presets while in the editor
3. moving the brush preset around and pressing the two buttons for reset and zoom
4. moving between engines that had previews and those that did not