Improve NuGet package

• Store assembly and .targets file in the build subdirectory of the project. Unfortunately it's not possible to create a subdirectory of the solution rather than the project. But it still improves things because it is now possible to include the .targets file without having to specify a version specific path.
• Add About dialog that shows the version of BuildDependencyManager.
• Allow comments in .dep file

Bugfixes

• adjustments for current TC version (9.1.x)
• don't crash if a project got renamed
• fix crash that happened in BuildDependencyManager when editing dependencies
• add Save menu item to BuildDependencyManager
• allow to specify filename on command line when opening BuildDependencyManager