adding IconicsCompatButton
Since IconicsButton is extending `android.widget.Button`, when I want to change color background, it messes up with buttons shape in apis before 21. Therefore, I think there is a need of adding `IconicsCompatButton`. Nothing is changed in the code, just it extends from AppCompatButton. Here's an example

``` java
import android.content.Context;
import android.os.Build;
import android.support.v7.widget.AppCompatButton;
import android.util.AttributeSet;

import com.mikepenz.iconics.Iconics;

public class IconicsCompatButton extends AppCompatButton {

    public IconicsCompatButton(Context context) {
        super(context);
    }

    public IconicsCompatButton(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public IconicsCompatButton(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public void setText(CharSequence text, BufferType type) {
        // NOTES:
        // 1. Need to disable the All Caps option to make Spannable work properly!
        // 2. This method will be called from the constructor of the super class
        if (Build.VERSION.SDK_INT > Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
            setAllCaps(false);
        }

        if (!isInEditMode()) {
            super.setText(new Iconics.IconicsBuilder().ctx(getContext()).on(text).build(), type);
        } else {
            super.setText(text, type);
        }
    }
}
```

I'm not sure if it's absolutely necessary though.
