EXT-3232 Refactoring: Improved the way of horizontal alignment of button's...

EXT-3232 Refactoring: Improved the way of horizontal alignment of button's image overlay. Now mLeftHPad/mRightHPad is used instead of mImageOverlayLeftPad and mImageOverlayRightPad. Also mImgOverlayLabelSpace/imgoverlay_label_space members was added to button.(h/xml) to define space between image overlay and button's label

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branch : product-engine