Bug 8092: Convert Koha::Cache to use CHI

Bug 8092: Convert Koha::Cache to use CHI

Implements cache handlers for Memcached, mmap shared-file persistent,
and in-process memory caches. If CHI is unavailable, Koha::Cache::Memcached
will fall back to using Cache::Memcached::Fast, or caching will be skipped
without croaking.

To test: run t/Cache.t with the following options, before and after
installing CHI:

2. Tests 3-9 should be skipped with the following:
export CACHING_SYSTEM=

2. You should receive two failures with the following if CHI is not installed:
export CACHING_SYSTEM=memory

3. You should receive two failures with the following if CHI is not installed:
export CACHING_SYSTEM=fastmmap

4. You will need memcached activated for the following to work (but it
   will work both with and without CHI):
export CACHING_SYSTEM=memcached
export MEMCACHED_SERVERS=127.0.0.1:11211
export MEMCACHED_NAMESPACE=KOHA

5. You should receive two failures with the following:
export CACHING_SYSTEM=thisdoesntexist

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Works as advertised, now we need a follow up to add the new dependency.

http://bugs.koha-community.org/show_bug.cgi?id=8029