EC-ISA: add intelligent table cache

Add persistent caching and sharing of encoding and decoding tables stored in a singleton object which are used/fillled by Isa CODEC instances. 
It looks like the get/put logic, including the lru cache handling belongs to the cache class rather than the ErasureCodeIsaDefault class. Moving the code there would also allo ErasureCodeIsaDefault to ignore the lock entirely since all it needs from the cache is a copy of a decode table, which does not require locking when used.