Align tiles between QSPanel and QSCustomizer

Give the tiles in QSCustomizer the same margin (half of
qs_tile_margin_horizontal in each side) and set the RecyclerView padding
to be the same as QSPanel's TileLayout margin. That way, the tiles align
when QSCustomizer opens (only in portrait) and the animation looks
better.

Test: manual, multiple densities
Fixes: 164207558
Change-Id: Ied960c9292c93c09f5ef04853d3b1a25bd778237