adding fixed version of all cmd practical on groups

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/adegenet@1195 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
added link to practical with solutions

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/adegenet@1196 edb9625f-4e0d-4859-8d74-9fd3b1da38cb