Fix the solution to include project using valid path

It seems that previous commits has spoiled the solution which currently shows
no projects. The patch fixes it by changing the path of included project to
existing one.
Adjust .gitignore file

The current .gitignore file doesn't contains rules for suo and user files. Also all files
from Debug and Release directories are found by git to be added. The patch fixes
all the mentioned issues.
Remove tests from main project

There are guidelines to keep tests away from the implementation.
Add new project for tests.

This patch adds new test project, moves all existing tests into new project and references
the newest stable version of NUnit. It also removes the binary files from the repository.
Remove unstable NUnit 2.9.6
Adjust build script and version number
Include NUnit.Runner and adjust build script
Migrate NAnt with contrib to NuGet packages
Adjust code after Ilker remarks

The side-by-side tests should remain because it was the intention of the author
to experiment with such kind of coexistence productive code and its tests.
Add developmentDependency="true" to packages.config

It should allow us consistent generating productive packages.
Merge pull request #4 from CHECK24/feature/PX-2101-Downgrade-NUnit

PX-2101 Downgrade NUnit to 2.6.3 and improve Nuget packaging