DbAccessor:
-Guarantees that access to Vertex and Edge is possible only through
Vertex::Accessor and Edge::Accessor.
-Guarantees that changing Vertex and Edge is possible only using
Vertex::Accessor returned by vertex_insert() method and
Edge::Accessor returned by edge_insert() method.
-Offers CRUD for Vertex and Edge except iterating over all edges.
Squashed commit messages:
First step in database accessor refactoring done.
It's compiling.
All tests with exception of integration_querys pass
Tests now initialize logging facilities.
Refactored accessors.
RecordAccessor now has 3 states.
From,To,Out,In in there respecive Accessors return unfilled RecordAccessor.
Added iterator classes into utils/itearator/.
Minor fixes to tests.
MultiIterator & MultiMap work.
There are some unfinished optimizations in the code commented.
All tests pass. Some common parts from tests have been moved.
