WIP: Review memory management in Gaudi

follow up of what was discussed during the 2017 Gaudi Workshop:

• PluginService must return std::unique_ptr
• component managers should be responsible for deleting the components
• reference counting should be dropped

So far I changed the plugin service factory signature, and adapted random number service and algorithm manager.

To actually make it work, I also had to modify the memory management of components and to make sure that the ApplicationMgr is actually destroyed at the end of the application. These changes overlap partially with !257 (closed).

Based on !701 (merged) for simplicity.