Refactor: Implement classic architecture with Repos and Services

[s-kostyuk]

Looks like we need to switch from current home-brew architecture to almost classical architecture with separate Repositories and Services.

For now the functionality of Services is entrusted to such entity as "ApiGateway". It control almost everything related to the of processing requests coming into different API implementations (like RestApi implementation). There is no separation of responsibilities between services based on functionality and a set of related objects.

The functionality of Repositories is entrusted to PlacementManager and BindingManager. Those two managers store and control access to Placements (the first one), Connections and Things (second one). Also they perform a small subset of functions usually entrusted to services like enabling and disabling of Things.

The last aspect to consider is a possibility to switch to Redis, SQLite or other lightweight databases for storing of persistent data (like settings of Things and Connections, like a set of Placements and Users and so on).

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Considering all mentioned information, to facilitate further development of the platform, the following decision was made:

• [x] create a set of abstract Repositories for each entity in the system;
• [x] create a set of Repository implementations that will use SQLite to store persistent data;
• [x] create a set of Repository implementations that will store data about Things and Connections in memory;
• [x] implement DTOs and DTO Builder for Things, Connections and Placements;
• [x] prepare declarations of interfaces for Services;
• [x] create a set of corresponding Services for managing Things, Connections and Placements;
• [x] replace current Managers with Services;
• [x] prepare everything needed to add user control policies and User management in the next (v0.3) release

[s-kostyuk]

Blocked by #33

[s-kostyuk]

Added 3 new tasks to the list:

• implement DTOs and DTO Builder for Things, Connections and Placements;
• prepare declarations of interfaces for Services;
• replace current Managers with Services

[s-kostyuk]

Reversal for a one of subtasks - see issue #30 to track further progress:

• create a set of Repository implementations that will use SQLite to store persistent data;

[s-kostyuk]

Closed one subtask - for now everything depends on further implementation of User Management in the next release:

• prepare everything needed to add user control policies and User management in the next (v0.3) release

[s-kostyuk]

All subtasks finished. Closing this issue for now.

Additional issues to monitor:

• 41 - Deprecate ApiGateway

• 38 - Deprecate UserManager

• 39 - Deprecate AuthManager

• 42 - Finalize ThingService implementation