feat(android): padding for Ti.UI.Button

[m1ga]

Currently Android only:

Adding padding to the Ti.UI.Button

Button 2 and 4 are default Ti buttons (without and with a custom background color). Currently there was no way to set a custom padding. Even worse: we've set the default padding for a button with background to a very small value for buttons with background color:

12.6.3.GA

(top: default color, bottom: custom background color).

Fix
This PR will set the default padding for a button with backgroundColor to the native padding again (first image, button 4) and gives the option to define a custom padding (first image, button 1 and 3).

Example

var win = Ti.UI.createWindow({layout:"vertical"});
var btn1 = Ti.UI.createButton({
	title: "just a text in a button",
	padding: {
		left: 50, right: 50, top: 20, bottom: 20
	}
});
var btn2 = Ti.UI.createButton({
	title: "just a text in a button",
});
var btn3 = Ti.UI.createButton({
	title: "just a text in a button",
	backgroundColor:"red",
	padding: {
		left: 50, right: 50, top: 20, bottom: 20
	}
});
var btn4 = Ti.UI.createButton({
	title: "just a text in a button",
	backgroundColor:"red"
});
btn2.addEventListener("click", function() {
	btn2.padding = {left: 50, right: 50, top: 20, bottom: 20};
});
btn4.addEventListener("click", function() {
	btn4.padding = {left: 50, right: 50, top: 20, bottom: 20};
});
win.add([btn1, btn2, btn3, btn4]);
win.open();

You can click Button 2 and 3 to test the property change.