HTML escape property documentation
HTML escape property documentation

Property documentation that contained text that looked like HTML
tags was getting passed through.  Use html/template instead of
text/template so that it gets escaped automatically.

Bug: 67909957
Test: manual inspection
Change-Id: I2050c34c04d7be3cdacd5a76967a739f9f837e89

google/blueprint,danw/blueprint,danw/blueprint,google/blueprint