Added support for specifying cache configuration
ref #176

Added a new setting THUMBNAIL_CACHE which defaults to 'default', but can be used to specify which cache configuration to use. This might be useful if running multiple cache clusters.

Signed-off-by: Rolf Håvard Blindheim <rolf@moota.com>
Missing implementation for the wand engine
Merge branch 'master' of github.com:rhblind/sorl-thumbnail into rhblind-master

* 'master' of github.com:rhblind/sorl-thumbnail:
  Added support for specifying cache configuration ref #176