Database Storage Engine Project M4 Basic implementation

= About the milestone=

This milestone includes coding (and documenting) the most important classes of the Database Storage Engine in order to have a testable prototype.

= Todo=
 * Write stubs and documentation for all API classes and methods (OK)
 * Write stubs for all non-API classes and methods (OK)
 * Implement the most important API-calls (OK)
 * Finish prototype (OK)