text_properties page improved

text_properties page improved

 * properties reordered for better grouping and priority
 * data and font_angle descriptions improved (noticeably about how to
   center the block on the pivot).
 * alignment: + applies to all columns
 * Examples: Extrawide MathML string wrapped.
 * See also improved: + xstring, label_properties, legend_properties,
   latex & mathML page; - set, get (too general)
 * History section created.
 * <emphasis> replaced with <literal> for better readability.
 * Other misc. styles improvements.

Change-Id: I95ac39a831e0be4c3f320e1246697be9c27378d2