Install private dlls in user directories
The message dll and resulttab dll should be placed in user directories. The resulttab dll is now installed by the vsix package in the package directory, and the message dll needs to be placed in the users private assemblies webtestplugins directory in order to load, rather than the all user shared privateassemblies folder (that also requires elevated rights). See https://msdn.microsoft.com/en-us/library/ff400224(v=vs.120).aspx