Add two new line selector types: solid colour and gradient. Solid colour only uses the primary colour setting.
The secondary colour setting is used for the gradient. Text colour for the selected item is also changeable.
These new settings are a bit controversial so they may be removed later.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@14868 a1c6a512-1295-4272-9138-f99709370657
