chore: Add entries to gitignore

.gitignore

@@ -24,6 +24,10 @@ bld/
 [Oo]bj/
 [Ll]og/
 
+# operating system junk files
+thumbs.db
+.DS_Store
+
 # Visual Studio 2015 cache/options directory
 .vs/
 # Uncomment if you have tasks that create the project's static files in wwwroot
@@ -294,3 +298,6 @@ src/GraphControl/GraphingImplOverrides.props
 !src/Calculator/TemporaryKey.pfx
 !src/CalculatorUnitTests/CalculatorUnitTests_TemporaryKey.pfx
 *.binlog
+
+# MFractors (Xamarin productivity tool) working folder
+.mfractor/