Documentation: clean up

-   /user/quick/desktop to bring together all common information for
    using Skia on desktop OSes.  Remove duplication.

-   Replace all instances of call ing gyp_skia directly with calling
    `python bin/sync-and-gyp`.  This is more correct on Windows

-   Remove outdated linux prerequisite packages

-   Formatting, formatting, formatting.

-   Note command-line syntax differences in Windows

-   SampleApp.app is no longer a bundle on MacOS

NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=1439493003

Review URL: https://codereview.chromium.org/1439493003
14 files changed