[Android] Implemented `sf::Window::hasFocus()`
Fixed right click not detected on OS X with trackpads, close #716

Now that `+[NSEvent pressedMouseButtons]` can be used, part of HIDInputManager becomes obsolete and is therefore removed.
Added static_cast for sf::Uint8 (fixes #731).
Reworked the UDev inclusion

* This fixes `SFML_DEPENDENCIES` missing the UDev library for static builds (issue #728).