Right click on long press; touch events on assets menu; fix for sticky :hover menus

Added support for mimicking right-click functionality on long press
- Added support for selecting a specific mouse button in fakeTouchEvent
- Modified the behavior of touch events so that mousedown with left click would not be triggered before it was certain a left click was desired
- Modified fakeTouchEvent so that the event provided would be read, rather than the current event
- This enables the storage of an event for later use, which allows us to choose between a left or right click based on how long the touch was held
Added simple touch handlers to assets menu. Somewhat surprisingly, this worked with no additional effort.
Fixed an issue where menus displayed on toolbar button :hover would remain visible despite touching outside the toolbar and sub-menu
- Removing :hover is not supported via js, but a rather dirty workaround is removing the :hover element from the DOM. This causes a tiny amount of flicker on the toolbar element, but in my opinion this is an acceptable tradeoff.

Oromis / touch20