Splitting the targets files into a properties and a targets file

#23
Adding the install.ps1 and uninstall.ps1 which will be used to add the imports to the project file.

#23
Adding the ability to a single additional template element for a specific template file

#23
Updating the NuSpec file templates

#23
Updating the nBuildKit settings.props file to match the default sample one.

#23
Merge pull request #23 from pvandervelde/issue/targetsandproperties

MsBuild.Projects: Split targets files into a targets and properties file