[MRM-1002] Website navigation links don't work as expected

[MRM-1002] Website navigation links don't work as expected
Submitted by: Jevica Arianne Zurbano

* replaced the breadcrumbs to point to the documentation's index to avoid
  o the directory listing when accessing http://archiva.apache.org/docs/
  o being pointed to a non-existing page like http://archiva.apache.org/docs/1.2-M1/docs/1.2-M1
* added 'Downloads' link in site.xml
* updated the evaluateBeanshell condition to coincide with site.xml modification

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@798430 13f79535-47bb-0310-9956-ffa450edef68