Set staring background color to black (Closes: #409) (#416)

    <style name="CalendarTheme.WithoutActionBar" parent="CalendarAppTheme">

        <item name="android:endYear">2036</item>

        <item name="android:startYear">1970</item>

        <item name="android:windowBackground">@color/bg_black</item>

    </style>

    <style name="CalendarTheme.WithActionBar" parent="CalendarAppThemeWithActionBar">