Don't hardcode the valid architectures in one xcode project

There's no reason to hardcode these here - these are the default.
(We keep the intentionally hardcoded default arch in the
codec_unittest project though.)
Use default paths for and object files and other intermediate files

This makes sure that one can build for all architectures without
having the intermediates from one clobber the other.
Update info file for bugzilla 1037754 - no longer need to advertise VP8.
Merge pull request #1192 from ethanhugg/info-file

Update info file for bugzilla 1037754 - no longer need to advertise VP8.
Merge pull request #1130 from mstorsjo/default-intermediates-path

Use default paths for and object files and other intermediate files
Merge pull request #1148 from mstorsjo/dont-hardcode-xcode-archs

Don't hardcode the valid architectures in one xcode project