Add center alignment for 2017 themes

Add "GLIF Pixel" theme that is a drop-in replacement for
SuwThemeGlif, which will center align the header and description
text.

To use GLIF Pixel theme, simply set the activity theme (using
android:theme or Activity#setTheme) to SuwThemeGlifPixel and use the
GLIF layouts normally.

Other theme attributes like status bar background will be done in a
separate CL.

Test: ./gradlew connectedAndroidTest test
Bug: 35446596
Change-Id: I3edee9cf80c1c84018ed08f47f9859e51a3936e6