Update Launcher to use theme colors.

Instead of using hard-coded variants of colors, use the theme color
that corresponds (colorAccent, colorPrimary, etc).

Updated:
- "Search for more apps" text
- App info drop target hover color
- PageIndicatorDots
- All apps & widget scroll bar & scroll popup colors
- All apps section text color
- widget picker background color

TODO:
- widget picker header color

BUG: 28625102
Change-Id: I74b543ff71b8caef8cd950c8183ac84c759cb4d5

src/com/android/launcher3/WidgetPreviewLoader.java

@@ -584,7 +584,7 @@ public class WidgetPreviewLoader {
                 // which would gets re-written next time.
                 mVersions = getPackageVersion(mKey.componentName.getPackageName());
 
-                Launcher launcher = (Launcher) mCaller.getContext();
+                Launcher launcher = Launcher.getLauncher(mCaller.getContext());
 
                 // it's not in the db... we need to generate it
                 preview = generatePreview(launcher, mInfo, unusedBitmap, mPreviewWidth, mPreviewHeight);