Create OSX Metal sample application

[AenBleidd]

Create a simple OSX application that uses Metal API and BOINC API.
References:

• https://developer.apple.com/documentation/metal/performing_calculations_on_a_gpu
• https://github.com/BOINC/boinc/tree/master/samples/example_app

Contact point: @AenBleidd

[brevilo]

Hi. Just to make sure I understand: I couldn't find any client/server support for Metal device detection/selection. Isn't that needed first before a sample (science) application can be made proper use of? Am I missing something?

Thanks