Update sample metadata tools for VS (#657)

Previously, the solution templates were named with .sln extensions. This caused Visual Studio to detect them as solutions when using the git browser. To prevent this, the solutions have been renamed to .slntemplate and the script has been updated to rename them to .sln in the output. I've confirmed that the template solutions no longer appear in Visual Studio.

Author: nCastle1

tools/metadata_tools/sample_metadata.py

@@ -328,6 +328,7 @@ def emit_standalone_solution(self, platform, sample_dir, output_root):
         # generate list of replacements
         replacements = {}
         replacements["$$project$$"] = self.formal_name
+        replacements[".slntemplate"] = ".sln" # replacement needed to prevent template solutions from appearing in Visual Studio git browser
         replacements["$$embedded_resources$$"] = "" # TODO
         replacements["$$nuget_packages$$"] = get_csproj_xml_for_nuget_packages(self.nuget_packages)
         replacements["$$code_and_xaml$$"] = get_csproj_xml_for_code_files(all_source_files, platform)