Add support for converting popular Android ARGB8888 format

As requested, replaces PR #2410 with a clean change history.

In a recent code review, I found two versions of this function in my code, so I thought it might be a useful addition. My code originally was Android-only before porting to libGDX, so perhaps others will be in this same situation and will find it convenient.
Merge pull request #2507 from mikemee/master

Add support for converting popular Android ARGB8888 format
Add variant of argb8888 method taking components
Add isOnscreenKeyboardVisisble to Input. Fix closing keyboard in iOS

Conflicts:
	backends/gdx-backend-robovm/src/com/badlogic/gdx/backends/iosrobovm/IOSInput.java