[ImageMagick] Set prefix, enable a few features
[ImageMagick] Set prefix, enable a few features

This change:

- Sets the --prefix option to configure so that the final artifact has
  the content we expect

- Sets PKG_CONFIG_PATH and depends on core/pkg-config to ensure we can
  enable features that require libraries to be configured via pkg-config

- Depends on libpng, xz and gcc-libs to enable a few more useful features
  in the built version of ImageMagick

- Sets pkg_lib_dirs and pkg_include_dirs so other plans can depend on
  imagemagick.

Signed-off-by: Steven Danna <9ce5770b3bb4b2a1d59be2d97e34379cd192299f@chef.io>

be-plans/be,be-plans/be,be-plans/be,be-plans/be