Themes: Add STYLE_THUMBNAIL to PreviewColumns

Change-Id: Ie18264cbede92220335400428e67735866cd442d
(cherry picked from commit c6c260e19de53aacdaaa6b76295af8e72f9311cb)
Themes: Add helper methods for creating complete component maps

These methods can be used to apply a theme while replacing any
components not found in the theme with the defaults.

Default components come from the default theme for the system
with any missing components in that default theme coming from HOLO.

Change-Id: Idea55cc684ccc8304b01a991c36b6993f55b8880
(cherry picked from commit 627b296cf36d744938429fcc0e45fc3664ad7a7c)