Bug 7248 follow-up (alternative)

Bug 7248 follow-up (alternative)

This patch introduces some new features for caching system:
* the type of caching is retrieved from ENV variable in httpd configuration if not forced when the ->new() is called.
* if $ENV{DEBUG} is ON, you'll have feedback when something is set or read from cache
* the Koha::Cache->is_cache_active is now available and will return 1 if there is a caching system available. It's a replacement for C4::Context->ismemcached
* fixes the mistake for debug/compress_threshold and expire_time parameters

The 2 report web service modules have been updated to use this new API

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>