Deprecate AuthManager

[s-kostyuk]

Create a new Service which will manage user authentication, access token management, access control and policies

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UPD:

OK, there are some things to do:

• [x] define an entity that will represent access tokens;
• [x] define a repository of access tokens;
• [x] create a service for auth and token management

[s-kostyuk]

Access token will be saved in Session objects (see commit 7c5cc3b)

[s-kostyuk]

Session objects will be managed by a SessionService (203ebcc). Authentication, authorization and password management will be handled by an AuthService (795ef8b)

[s-kostyuk]

OK. Looks like it's finished but needs a LOT of testing: #58. Will be merged after #56 will be marked as completed