Fixed GraphHandler returning wrong object type. Closes #75

This also fixes wrong object type (besides document) being returned on get(), getById()

Written tests and updated some old ones.

Updated CHANGELOG
Fixed test that was not removing test graphs in the database on teardown.
Updated CHANGELOG
Merge pull request #112 from frankmayer/devel

Bug Fixes mainly involving returned object type
Re-implemented statistics according to new implementation in ArangoDB 1.3. Fixes #106

Updated tests

updated CHANGELOG
Merge pull request #113 from frankmayer/devel

Reimplemented statistics according to new implementation in ArangoDB 1.3