make LinearColorBar themeable

Move colors to resources and use them instead.

Change-Id: I923e5daa219f302dc24e62faab666483109e6620
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
Fix NullPointerException issue when user change

When info is null, we have risk to have access null point.

Change-Id: Ie6acee5c99d6297e31d46585435a735a38b19e82