Update HomeScreen for CES 2018 demo

Update HomeScreen for CES 2018 demo

- HomeScreen's color scheme has been changed from green to blue based.
- Introducing the default icon
- Bug fixes.

Related commits:
096c072 Apply LinearGradient to first letters drawn when icon is missing
a7e1f83 Fix installation info
228a3ff Fix volume slider in the media area didn't work
96c3e6d Display blank icon with first letter in new color scheme
f756a01 Change to new color scheme
242e1fc Display a blank icon with first letter when icon is not exist

Bug-AGL: SPEC-673

Change-Id: I6845e9fe53f722edaf7e45ff007e246c47dc0345
Signed-off-by: Tadao Tanikawa <tanikawa.tadao@jp.panasonic.com>