Scan for .licenseheader files using the folder hierarchy of the .csproj and .sln

[jbennink]

Currently the .licenseheader file is searched in the csproj folder and optionally in the solution folder. For source-code with multiple solutions and a lot of projects it would be very convenient if the .licenseheader files was searched for in the project folder, and then recursively up the folder hierarchy.
That way you can put a "global" .licenseheader file in the solution/workspace root and only have to put additional .licenseheader files in sub-folders when you want to change the default behaviour. It would be even better if, after locating the root-folder, settings are applied from that folder downward applying .licenseheader settings in order so that "deeper" folders could set more specific settings.