Add System.Diagnostics.Switch/etc. to the MOBILE profile.

Followup to:

	http://forums.xamarin.com/discussion/comment/11823/#Comment_11823

These are Switches with a labotomy: the MOBILE profile does not
support System.Configuration.dll, so there is no support for
.exe.config files or
System.Diagnostics.DiagnosticsConfigurationHandler.

Consequently these Switches are largely a compatibility/portability
aid: they DO NOT have the full functionality that the desktop
profile affords. Specifically, there is no way to provide an XML
config file that contains the Switch values to use. If you need to set
the Switch values, this MUST be done manually, e.g. through a Switch
constructor's `defaultSwitchValue` parameter or through a property,
e.g. for SourceSwitch:

	http://msdn.microsoft.com/en-us/library/w65awck1.aspx
	http://msdn.microsoft.com/en-us/library/system.diagnostics.sourceswitch.level.aspx