Allow a different state directory for hydra-server

Dependencies

• [2] EKHL23VI Keep sessions for a week
• [3] VBUNNYXG Fix path to the session data
• [4] HSVVEKTY * Start of a JSON API to get information about a specific build.
• [5] E3M46H7T Keep session state across hydra-server restarts
• [*] J5UVLXOK * Start of a basic Catalyst web interface.

Change contents

• replacement in src/lib/Hydra.pm at line 58
  [2.34]→[3.0:69](∅→∅),[3.649]→[3.0:69](∅→∅)
  − storage => Hydra::Model::DB::getHydraPath . "/session_data",
  [2.34]

  [3.69]
  + storage => ($ENV{'HYDRA_SERVER_DATA'} // Hydra::Model::DB::getHydraPath) . "/session_data",