New interface for algorithm's `suggest()` and `observe()` methods.

Algorithm interface for suggest() and observe() is changed to use trials instead of list of points. This will provide more flexibility when designing new algorithms. There is no impact for users, except for algorithm plugins that will not be backward compatible with previous versions of Oríon.

The factory abstract class used to create database, storage, algorithm, adapters and parallel strategy has been redesigned to better support external implementations and be easier to debug. This redesign should also have no direct impact for users, except for backward compatibility issues with algorithm plugins for previous versions of Oríon.

🏗 Enhancements

• Improve resiliency of trial reservation @bouthilx (#693)
• Support batched promotions in ASHA @bouthilx (#689)
• Refactor algorithms observe/suggest to work on trial objects directly @bouthilx (#686)
• Rework factory @bouthilx (#681)
• Improve Getting started example command @Delaunay (#666)

🐛 Bug Fixes

• Avoid inf-loop in TPE.suggest @bouthilx (#680)