Implement and evaluate backends for different database.

[VladyslavUsenko]

• Implement util interface for several other database (PostgresSQL, MongoDB.. )
• Evaluate performance of the typical tasks with different databases. The tasks should include: saving keyframes, reading keyframes, reading keypoints, map optimization, map merging
• Play around with databases to evaluate performance of different optimizations (indexes, different database structure..)
• Make evaluation plots and conclusion about the best database for storing and processing mapping information.