Re #8475 - Connection to the RestAPI
Re #8476 - Implemented `list_certificates` with unit tests.
Re #8476 - Auxiliary script for database initialization, FileAnchor
Re #8471 - Added name of tables to constants- TAB_CERTIFICATE_TYPES for CertificateTypes table- TAB_USAGE_TYPES for UsageTypes table
Re #8471 - Added comments for CRUD functions
Re #8471 - Tested direct DB communication- implemented tests for Certificates and PrivateKeys tables via DBManager
Re #8471 - Added FK of parent certificate
Re #8471 - Edited constants
Re #8471 - Created constants of DB names- Constant for each of names in DB (table, column)
Re #8471 - Implemented DB communication- implemented operations create, read, update, delete- created file with constants contains name of DB file and default values in DB