Don't code sign by default.
Don't code sign by default.

This adds a argument to configure for whether to code sign the
framework.  This allows lone developers to not code sign if not needed,
but allows official builds to be signed.

Closes #90

Change-Id: I94223aeb1e189fcbc3e98f08834ec94dc7c2b85a

shaka-project/shaka-player-embedded,shaka-project/shaka-player-embedded,shaka-project/shaka-player-embedded,shaka-project/shaka-player-embedded,shaka-project/shaka-player-embedded