Better ortholog cache

[gcornut]

For now the cache is in memory and grows indefinitely
TODO

• Add cache persistance (to disk)
• Flatten cache for easier management
  {:org {:prot :ortho-group}} => {[:org :prot] :ortho-group}
• Set up caching strategy
• Link memory cache, disk cache and inparanoid webservices all together

Pseudo-code:

(if in-memory-cache?
   (get-from-memory-cache)
   (save-in-memory-cache
     (if in-disk-cache?
        (get-from-disk-cache)
        (save-in-disk-cache
          (get-from-inparanoid-ws)))))

Proposed caching strategy:

• LRU with size threshold (with clojure core.cache)
• Write to memory and disk on new entry (or periodically write to disk?)

Persistence:

• Use nippy for writting/reading clojure data structures in binary
• Split the cache in organism pairs (like in PMB)

TODO cache loader:

• Download OrthologXML by organism pairs
• Parse & load to cache
• Add approx loaded percent
• Add progress monitoring interface