reduce shine on glasstitlebar

It tries to address the legibility of the current shade of white introduced at https://github.com/BigNoid/xbmc/commit/7e99e8cae2cedd5234d1b72bf94a2373c0da1a80 vs existing GlassTitleBar.png

Reduced GlassTitleBar.png shine to 70% of existing file values to try address this problem.

Address the comments of @bignoid made to https://github.com/xbmc/xbmc/issues/3935