[cmake] Use latexmk

doc/CMakeLists.txt

 add_subdirectory(doxygen)
 
-dune_add_latex_document(istl.tex
-  FORCE_DVI
-  BIBFILES istl.bib
-  IMAGES blockstructure.eps)
-create_doc_install(istl.pdf
-  ${CMAKE_INSTALL_DOCDIR} istl_safepdf)
+dune_add_latex_document(
+  SOURCE istl.tex
+  FATHER_TARGET doc
+  INSTALL ${CMAKE_INSTALL_DOCDIR})