minimum/maximum value keys should be min/max

[chriscox]

The web remote controller cannot create a slider as these values are not consistent across platforms and as defined in our API docs:

static NSString *const RMXDictionaryKeyMinValue = @"minimumValue";
static NSString *const RMXDictionaryKeyMaxValue = @"maximumValue";

should be

static NSString *const RMXDictionaryKeyMinValue = @"minValue";
static NSString *const RMXDictionaryKeyMaxValue = @"maxValue";