Gallery2: support GIF animation

(cherry picked new files from commit
2b133c9747af26701a12d60caef3e7e14cf55536)

Change-Id: I227cef76cbacd66b7e87bc59b4f07d518b70a859
Gallery2: support GIF animation

This change implements a Java GIF decoder.

Change-Id: I72b6e8eb25572bba77a2a46e1754d8db8c47a0cc
CRs-Fixed: 517575