#185 fix

[TikhomirovSergey]

Fixed #185

@FindBy(locator)
MobileElement element;
...


(AndroidElement) element..//if now test of an Android app is being run
//or
(IOSElement) element..//if now test of an iOS app is being run

Also now there is something like... bounding. It means that user is not allowed to declare IOSElement field for Android-specific scripts/pageobjects and AndroidElement field for iOS-specific scripts/pageobjects.

• Additional change:
  An ability to declare TouchableElement field has been added.

@FindBy(locator)
TouchableElement element;
...