Update the .gitignore file

The .gitignore file was updated to exclude the nuget.exe file and to be
cleaner.
Delete the nuget.exe file

This file will be downloaded automatically when source is compiled.
Set the nuget.exe to be downloaded

This commit set the value of DownloadNuGetExe to true to automatically
download the nuget.exe file.
Exclude the .nuget folder from solution explorer

Excluding the folder does not causes any side effect.
Update the .gitignore file

Binary files(*.dll, *.exe) are ignored from git repository.