Pages like the new tab page, error page, etc. all belong solely to
Ladybird, but are scattered across a couple of subfolders in Base. This
moves them all to Base/res/ladybird.
Note that this fixes contradictory default values for group
"Preferences", key "Home". This is exactly the kind of errors I want to
prevent with this new style.
The hope is that this can later be used to:
- verify that all accesses to the same key use the same default value,
- and extract the default values more easily.
