[TIMOB-17363] Android: Add "Ti.UI.MaskedImage" support

*Original Request:* As of Android 5.0 (aka: Android L) you can define bitmaps as an alpha mask and tint them using a color resource. You create these assets only once and color each instance to match your theme. This is done via a Java Drawable class' setTint(), setTintList(), and setTintMode() method. https://developer.android.com/reference/android/graphics/drawable/Drawable.html#setTint(int) *Proposed Solution:* This should be implemented via our existing Ti.UI.MaskedImage feature which is currently iOS only. This way we have parity between platforms. https://docs.appcelerator.com/platform/latest/#!/api/Titanium.UI.MaskedImage The concept is exactly the same. You apply a color or image to a grayscaled mask and specify the PorterDuff compositing mode. https://developer.android.com/reference/android/graphics/PorterDuff.Mode.html Instead of using Android 5.0's tinting APIs, we should use Android's Drawable and Canvas classes instead which support tinting/masking in all Android OS versions. _(The new tinting methods are there out of convenience for a pre-existing feature.)_ *Note:* This feature would also provide an alternate solution for developers who want to display an ImageView with rounded borders. Since rounded borders have known hardware acceleration bugs on Google's end, an alternative solution is to use a MaskedImage with a circular mask instead. This is how it's usually done by native Android developers anyways.