Move SkGammaColorFilter to tools, limit to sRGB

Similarly, limit GrGammaEffect to sRGB (and rename it).

BUG=skia:

Change-Id: I88feef11ab7040bca2fa4c2eed71923ded87a0d0
Reviewed-on: https://skia-review.googlesource.com/7375
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
16 files changed