One database for all tests

[Lenkelheit]

Description

Setted up and fixed one database for all tests. Some tests were rewritten without using the entities' id, because they caused fails. Added connection string to App.config for tests. Fixed #72, fixed #70, fixed #69.

Type of change

• [X] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] My code builds clean without any errors or warnings

[iamprovidence]

Its also seems like you close #69