HTTP response cache for conditional request against the GitHub API

[soul2zimate]

Since aphrodite-0.5.0.Final, it switched to new github-api http://github-api.kohsuke.org/ which supports https://developer.github.com/v3/#conditional-requests with a local cache. pull-request-processor should do same thing as prbz-overview.

it should add some system parameters as defined in https://github.com/jboss-set/aphrodite#cache-configuration. Otherwise, it will not use any cache.

current cache directory on thunder is /home/jboss/cache/github-cache
cache dir is "/home/jboss/cache", cache name is "github-cache" and size is "20" (M)