Add missing standard file header.
Add license acceptance dialog.
Scroll multiple packages in license accept dialog.
Fix blank summary in license accept dialog.

Use description if the package summary is missing.
Add select projects dialog.
Highlight disabled projects in light grey in Select Projects dialog.
Prevent disabled project being selected in Select Projects dialog.
Prevent disabled projects being selected by the mouse.
Merge branch 'master' of https://github.com/mrward/monodevelop-nuget-addin