ofxiOSGetDeviceInfo for querying device type and major / minor versions. 

As discussed in #2872 

This is a more future proof approach for determining version of iOS devices ( vs the older approach of listing every single possible device i.e.: OFXIOS_DEVICE_IPHONE_3GS  OFXIOS_DEVICE_IPHONE_3GS_CHINA etc ) 

It returns ofxiOSDeviceInfo which contains device type, device string and major and minor versions of the device. 
In the future we could add more info to ofxiOSDeviceInfo i.e.: `bHasCamera` `bRetina` etc 

Here is how it currently works with the an iPhone 5 and the simulator. 

    ofxiOSDeviceInfo info = ofxiOSGetDeviceInfo();
    cout << "device type " << (int)info.deviceType <<endl;
    cout << "device string " << info.deviceString <<endl;
    cout << "versionMajor " << info.versionMajor <<endl;
    cout << "versionMinor " << info.versionMinor <<endl;

    device type 0  // ( OFXIOS_DEVICE_IPHONE )
    device string iPhone5,2
    versionMajor 5
    versionMinor 2

    device type 0 // ( OFXIOS_DEVICE_IPHONE )
    device string iPhone Simulator
    versionMajor 0
    versionMinor 0

pinging @julapy @admsyn