Adds a toLatex method for the sts-class

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@721 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Adds unitTests for toLatex method

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@722 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Moves test files for toLatex method

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/surveillance@723 edb9625f-4e0d-4859-8d74-9fd3b1da38cb