Add new attr to control SeekBar mark always show

[qiujuer]

Now, we need SeekBar Indicator marker is always show

ok, we need attrs:

        <attr name="gIndicator">
            <enum name="always" value="-1" />
            <enum name="none" value="0" />
            <enum name="auto" value="1" />
        </attr>

[qiujuer]

Will do it on 2.0.0 up.