Fix generating LaTeX formula images
* lisp/ox-odt.el (org-odt--translate-latex-fragments): Fix imagemagick support.
* lisp/ox-html.el (org-html-latex-environment)
(org-html-latex-fragment): Fix imagemagick support.
* org.el (org-create-formula-image-with-imagemagick): Generate correct
size formula image.
(org-format-latex-header): Change pagestyle command position.
* doc/org.texi (@LaTeX{} fragments)
(Previewing @LaTeX{} fragments)
(Math formatting in HTML export)
(Working with @LaTeX{} math snippets): Add document about creating
formula image with imagemagick.