expand imageinfo in C api, start on colorspace

After sk_imageinfo was initially created, we have added a colorspace to it,
and that object is a smart-pointer. In response to that, this CL upgrades
imageinfo to an "object" (like paint), so we can manage the ref-counting of
its colorspace, and to allow for future changes/expansion (like paint).

Bug: skia:
Change-Id: I629ff99c0820fdbe83f062d9fb768c15cda68e18
Reviewed-on: https://skia-review.googlesource.com/157156
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
8 files changed