Add cached session

[zferentz]

Add simple caching (in memory, not redis/memcache) .

When we get a new connection - if we have "cached data" - return the cached
data (and don't even bother opening a socket to the server).

If we don't have cached data - operate just like standard session however
keep the data from the server in a cache. Note that we're storing in the
cache only when the connection is closed (to avoid partial data) !!!!