Fix for issue #106

The cause was the fact that some error messages go through two string.Format(...) stage (ugly, no better approach identified yet), so string with curly braces raised unexpected errors on the second stage.
Fixed by ensuring curly braces are doubled when necessary. Secure fix implies creation of a new API to generate custom summary messages.

Ignore TimeZone related tests when TimeZone is not found, as it is a indication the current OS is not windows. 

**Note** coded on Xamarin, so no stylecop or test coverage availalable