Added default SQLite Database

This database is used for persistent storage of user settings, account
settings and messages.
Updated Class Diagram
Added Database Diagram
Updated Doxyfile
Changed to unencryted database
Added Toolbox class for helper methods
Added Constants class to hold constants
Changed type for date property

Added documentation for messageId property
Changed name of Account Name property
Implemented database funtionality

Added support for fetching all accounts from database.
Added support for inserting an account to the database.