New interface for cacheable objects

Signed-off-by: selmeci <selmeci.roman@gmail.com>
Worker cache return value of command evaluation only if cache UID is
returned

Signed-off-by: selmeci <selmeci.roman@gmail.com>
Added element type specification

Signed-off-by: selmeci <selmeci.roman@gmail.com>
Merge branch 'master-zeromq' into element-attribute-service-loadbalancer

Conflicts:
	src/com/infones/edocu/communication/cache.clj
	src/com/infones/edocu/communication/worker.clj

Signed-off-by: selmeci <selmeci.roman@gmail.com>