This moves all of the Backend classes into a separate package from the
main framework, and uses it's __init__.py to allow some predefined
objects from all of the packages to be accessed directly through
backends. This API should be sufficient for most applications. It is
possible to directly access the modules in the backends package.

In many of the cases where we need to bypass the backends package API
the code accessing could use refactoring. Some of this refactoring will
be done by this series.

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>