Fix hover on touch devices

[TheSeally]

Fix #1506

1. Add hover class

• change implementation of hovering button from CSS hover to hover class
• add new property to Button class constructor which shows is shortcut needed
• add default behaviour for buttons with shortcuts

2. Add touch functionality

• add touchstart and touchend function;
• when player touch button and after it move finger more than 50px click event doesn't happen

[DreadKnight]

@TheSeally Great job, this really makes the difference!
Only one thing could improve this imo, but I've opened a different issue for it #1527

[TheSeally]

Thank you for the opportunity to participate in opensource project. I'm glad to help your project.
I try to take issue #1527 later

[DreadKnight]

Cool, if you can manage that issue as well, awesome! Otherwise there are plenty of other open issues that I greatly struggle with as a crappy coder that I am :D