Added HasClaim, FindFirst, FindAll into ClaimsPrincipal

Added HasClaim, FindFirst, FindAll System.Security.Claims.ClaimsPrincipal method overloads - This change in released under the MIT license.

This addresses [Bug 22065](https://bugzilla.xamarin.com/show_bug.cgi?id=22065)
Add a space before the opening parenthesis to adhere with the [Mono Coding Guidelines](http://www.mono-project.com/Coding_Guidelines).

This applies to the rest of the PR as well.