bootanimation: implement split packaging of animation

Animation package zip can be separated into OEM and SYSTEM
OEM desc.txt can use new command "$SYSTEM" to invoke animation
from SYSTEM package

Changes to animation structure:
1. animation can refer other animation
2. animation contains zip file reference
3. BootAnimation has name of root of animation Zip; processing desc.txt we
need filename of container zip and we can't access it from ZipFileRO instance

movie() changes:
1. Split movie() into loading Zip and playing part
2. load parses desc.txt and if needed referred Zip
3. play can descend animations tree

Change-Id: I600d02c84d537df7b3e32a84f84a294b26e319e0
Signed-off-by: Andriy Naborskyy <andriyn@google.com>