add background image support to newtab page

also:
- updates styling on some newtab page elements
- centres search bar vertically when other elements are disabled
- adds new tweak: hide Firefox logo on newtab page

.gitignore

@@ -4,3 +4,8 @@ inkscape-template.svg
 /userContent.css
 .vscode
 /icons
+/chrome/background-0.jpg
+/chrome/background-1.jpg
+/chrome/background-0.png
+/chrome/background-1.png
+/custom/