Packages, bin and obj are excluded from git repository

I think it's a best practice to exclude binary artefacts from the repository.

Those files can be generated by the build procedure, and including them in the repository is pretty unnecessary.
They consume space and since their binary nature, they are usually very hard to diff.

For example, this is [the standard ```.gitignore``` proposed by @GitHub](https://github.com/github/gitignore/blob/master/VisualStudio.gitignore#L17-L19): it excludes every files in ```bin``` and ```obj```. The same does the site [gitignore.io](https://www.gitignore.io)

Microsoft even published a tool called [Clean Projects](https://code.msdn.microsoft.com/windowsdesktop/Clean-Cleans-Visual-Studio-a05bca4f) that can be used to remove binaries from a solution before its distribution.

The same should apply to ```packages```: they are automatically downloaded by MSBuild via NuGet when the Solution is opened: in this case as well, including them in the solutions is just superfluous.


This PL contains a bunch of deletions, and the inclusion of the directories ```packages```, ```bin```, and ```obj``` in ```.gitgnore```, so that further modifications to those files won't be included in the next commits.