Add performance tests for all of the benchmarked things (and a few others)
Add support for running Objective-C tests on devices

Swift tests are exploding horribly on iOS 7.0, and I have been unable to
get Xcode to actually deploy working apps to iOS 8.0, so no swift
testing on devices for now.
Build in release mode when running tests on a device

Performance numbers for debug builds aren't very interesting.
Merge pull request #758 from realm/tg-device-tests

Add some performance tests and support for running them on devices